Method and device for transceiving frame in wireless lan system

ABSTRACT

Provided is a method and device for transceiving a frame in a wireless LAN system. Particularly, an AP transmits a first frame to a first STA via a first band. The AP receives a second frame from a second STA via a second band while the first frame is being transmitted. The first band and the second band are combined with each other as a multi-band. The multi-band simultaneously supports a DL transmission and a UL transmission. The relationship between the first STA and the second STA is a hidden node. A PHY header of the first frame includes channel status information of the second band. An NAV of the first STA is set up on the basis of the channel status information.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a technique for transmitting and receiving a frame in a wireless local area network (WLAN) system and, more particularly, to a method and a device for transmitting channel state information on a multi-band in a WLAN system.

Related Art

Discussion for a next-generation wireless local area network (WLAN) is in progress. In the next-generation WLAN, an object is to 1) improve an institute of electronic and electronics engineers (IEEE) 802.11 physical (PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHz and 5 GHz, 2) increase spectrum efficiency and area throughput, 3) improve performance in actual indoor and outdoor environments such as an environment in which an interference source exists, a dense heterogeneous network environment, and an environment in which a high user load exists, and the like.

An environment which is primarily considered in the next-generation WLAN is a dense environment in which access points (APs) and stations (STAs) are a lot and under the dense environment, improvement of the spectrum efficiency and the area throughput is discussed. Further, in the next-generation WLAN, in addition to the indoor environment, in the outdoor environment which is not considerably considered in the existing WLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium, Hotspot, and building/apartment are largely concerned in the next-generation WLAN and discussion about improvement of system performance in a dense environment in which the APs and the STAs are a lot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in an overlapping basic service set (OBSS) environment and improvement of outdoor environment performance, and cellular offloading are anticipated to be actively discussed rather than improvement of single link performance in one basic service set (BSS). Directionality of the next-generation means that the next-generation WLAN gradually has a technical scope similar to mobile communication. When a situation is considered, in which the mobile communication and the WLAN technology have been discussed in a small cell and a direct-to-direct (D2D) communication area in recent years, technical and business convergence of the next-generation WLAN and the mobile communication is predicted to be further active.

SUMMARY OF THE DISCLOSURE

The present disclosure proposes a method and a device for transmitting and receiving a frame in a wireless local area network (WLAN) system.

An embodiment of the present disclosure proposes a method for transmitting and receiving a frame.

The embodiment may be performed in a network environment supporting a next-generation WLAN system. The next-generation WLAN system may be a WLAN system evolving from an 802.11ax system and may satisfy backward compatibility with the 802.11ax system. The next-generation WLAN system may correspond to an extremely high throughput (EHT) WLAN system or an 802.11be WLAN system.

The embodiment proposes a method for sharing a channel state to solve a hidden node problem when flexible DL/UL transmission using multi-band aggregation is performed in a next-generation WLAN, such as an EHT WLAN system.

The embodiment may be performed by an access point (AP), and a first station (STA) and a second STA of the embodiment may correspond to STAs supporting an EHT WLAN system. The AP and the first STA may support a multi-band (or multi-link).

The AP transmits a first frame to the first STA through a first band.

The AP receives a second frame from the second STA through a second band while transmitting the first frame.

The first band and the second band may be aggregated into a multi-band. The first band includes a first primary channel, and the second band includes a second primary channel.

When the multi-band includes only the two bands which are aggregated, the first band may be a 2.4 GHz or 5 GHz band, and the second band may be a 6 GHz band. When the multi-band further include a third band, the first band may be a 2.4 GHz band, the second band may be a 5 GHz band, and the third band may be a 6 GHz band. The foregoing configurations of the bands are provided only for illustration, and the WLAN system may support various numbers of bands and channels.

The multi-band simultaneously supports DL transmission and UL transmission. This is called flexible DL/UL (FDU) transmission, and FDU transmission is a transmission technique enabling simultaneous Tx/Rx in a multi-band to increase average BSS throughput.

The first STA and the second STA are in a hidden node relationship. Thus, the first STA cannot recognize transmission by the second STA through the second band. If the first STA transmits a third frame through the second band, a collision with the second frame transmitted by the second STA occurs. This embodiment proposes a method of sharing channel state information on a different band in a specific band in order to prevent a data collision between STAs in a hidden node relationship. Here, the channel state information is included in a physical (PHY) header in order to share the channel state information with all STAs within BSS coverage.

Specifically, a PHY header of the first frame includes channel state information on the second band. Accordingly, a NAV for the first STA is configured based on the channel state information.

For example, when the channel state of the second band is idle based on the channel state information, the NAV for the first STA may not be configured. In this case, it is assumed that no frame is transmitted in the second band while the first frame is being transmitted. Since the channel state of the second band is idle, the first STA may transmit the third frame through the second band without needing to configure a NAV.

In another example, when the channel state of the second band is busy based on the channel state information, the NAV for the first STA may be configured until the transmission of the first frame ends, which means that since the second frame is received in the second band while the first frame is being transmitted, the channel state of the second band is busy. Accordingly, the first STA configures the NAV, thereby not transmitting the third frame through the second band until the transmission of the first frame ends.

The PHY header may further include transmission duration information on the multi-band.

The transmission duration information may include a granularity subfield and a duration subfield. The maximum length of the duration subfield may be determined based on the value of the granularity subfield. For example, when the value of the granularity subfield is 64 us and the duration subfield is 4 bits, the maximum length that can be indicated by the duration subfield may be 15*64=960 us.

The duration subfield may include first duration information or second duration information.

The first duration information may be information on the length of transmission duration of the second frame excluding Td. The second duration information may be information on the length of a transmission opportunity (TXOP) for the second STA excluding Td.

Td may be a length equal to the difference between the transmission start time of the second frame and the transmission start time of the first frame. That is, the transmission duration information may include information on the length (time) of a frame or TXOP duration excluding Td rather than including a frame or TXOP duration value as it is.

The NAV for the first STA may be set to be equal to the length of the first duration information (duration of the second frame—Td) or the length of the second duration information (TXOP duration of the second STA—Td).

The AP may receive the third frame from the first STA through the second band after the NAV for the first STA. Accordingly, the first STA may transmit the third frame through the second band without a collision with the second frame.

Hereinafter, a signaling method for multi-band aggregation is described. In this embodiment, configuration information on the multi-band is described as being received, and signaling may be performed by employing an FST setup method.

A transmission device and a reception device to be illustrated below may correspond to the AP or the first and second STAs illustrated above. The transmission device may transmit a multi-band setup request frame to the reception device. The transmission device may receive a multi-band setup response frame from the reception device.

The transmission device may transmit a multi-band ACK request frame to the reception device. The transmission device may receive a multi-band ACK response frame from the reception device.

The transmission device may include a first station management entity (SME), a first MAC layer management entity (MLME), and a second MLME. The reception device may include a second SME, a third MLME, and a fourth MLME.

The first MLME and the third MLME may be entities supporting the first band, and the second MLME and the fourth MLME may be entities supporting the second band.

The multi-band setup request frame and the multi-band setup response frame may be transmitted and received between the first MLME and the third MLME. The multi-band ACK request frame and the multi-band ACK response frame may be transmitted and received between the second MLME and the fourth MLME.

The first and the second SMEs may generate a primitive including a multi-band parameter. The multi-band parameter may include a channel number designated in the multi-band, an operating class, and a band identifier (ID). The primitive may be transmitted to the first to fourth MLMEs.

When the FST setup method is employed for the multi-band aggregation, the FST setup method includes four states and a rule for a method of transitioning one state to a next state. The four states are Initial, Setup Completed, Transition Done, and Transition Confirmed states.

In the Initial state, the transmission device and the reception device communicate in an old band/channel. Here, when an FST setup request frame an FST setup response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Setup Completed state and are ready to change the currently operating band/channel(s). An FST session may be entirely or partially transferred to another band/channel.

When an LLT value included in the FST setup request frame is 0, the transmission device and the reception device transition from the Setup Completed state to the Transition Done state and are allowed to operate in different bands/channels.

Both the transmission device and the reception device need to succeed in communication in a new band/channel to reach the Transition Confirmed state. Here, when an FST ACK request frame and an FST ACK response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Transition Confirmed state and establish a complete connection in the new band/channel.

According to an embodiment proposed in the present disclosure, to solve a hidden node problem that may occur in flexible DL/UL transmission in a multi-band, channel state information on each band may be transmitted, thereby reducing the probability of a collision and enabling efficient data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wireless local area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEE standard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) used in a band of 20 MHz.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) used in a band of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) used in a band of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B according to an embodiment.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a common information field.

FIG. 11 illustrates an example of a sub-field being included in a per user information field.

FIG. 12 illustrates an example of an HE TB PPDU.

FIG. 13 illustrates multiple channels allocated in a 5 GHz band.

FIG. 14 illustrates four states of an FST setup protocol.

FIG. 15 illustrates a procedure of an FST setup protocol

FIG. 16 illustrates an example of multi-band aggregation using a 2.4 GHz band and a 5 GHz band.

FIG. 17 illustrates an example in which a primary channel exists in each band (or RF) when performing multi-band aggregation.

FIG. 18 illustrates an example of a FDU transmission method.

FIG. 19 illustrates a hidden node problem that occurs in a FDU transmission method.

FIG. 20 illustrates an example of setting a NAV value based on multi-band CCA information.

FIG. 21 illustrates an example of a field defined to share multi-band transmission duration information.

FIG. 22 illustrates an example of sharing PPDU duration in an FDU transmission method.

FIG. 23 illustrates an example of sharing a TXOP in an FDU transmission method.

FIG. 24 illustrates an example of an operation process of a new control frame.

FIG. 25 is a flowchart illustrating a procedure in which a transmission device transmits and receives a frame according to an embodiment.

FIG. 26 is a flowchart illustrating a procedure in which a reception device transmits and receives a frame according to an embodiment.

FIG. 27 is a diagram illustrating a device for implementing the aforementioned method.

FIG. 28 illustrates a specific wireless device for implementing an embodiment of the present disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wireless local area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructure basic service set (BSS) of institute of electrical and electronic engineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may include one or more infrastructure BSSs (100, 105) (hereinafter, referred to as BSS). The BSSs (100, 105), as a set of an AP and an STA such as an access point (AP) (125) and a station (STA1) (100-1) which are successfully synchronized to communicate with each other, are not concepts indicating a specific region. The BSS (105) may include one or more STAs (105-1, 105-2) which may be joined to one AP (130).

The BSS may include at least one STA, APs providing a distribution service, and a distribution system (DS) (110) connecting multiple APs.

The distribution system (110) may implement an extended service set (ESS) (140) extended by connecting the multiple BSSs (100, 105). The ESS (140) may be used as a term indicating one network configured by connecting one or more APs (125, 130) through the distribution system (110). The AP included in one ESS (140) may have the same service set identification (SSID).

A portal (120) may serve as a bridge which connects the wireless LAN network (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network between the APs (125, 130) and a network between the APs (125, 130) and the STAs (100-1, 105-1, 105-2) may be implemented. However, the network is configured even between the STAs without the APs (125, 130) to perform communication. A network in which the communication is performed by configuring the network even between the STAs without the APs (125, 130) is defined as an Ad-Hoc network or an independent basic service set (IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating the IBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operates in an Ad-Hoc mode. Since the IBSS does not include the access point (AP), a centralized management entity that performs a management function at the center does not exist. That is, in the IBSS, STAs (150-1, 150-2, 150-3, 155-4, 155-5) are managed by a distributed manner. In the IBSS, all STAs (150-1, 150-2, 150-3, 155-4, 155-5) may be constituted by movable STAs and are not permitted to access the DS to constitute a self-contained network.

The STA as a predetermined functional medium that includes a medium access control (MAC) that follows a regulation of an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface for a radio medium may be used as a meaning including all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), user equipment (UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used in various meanings, for example, in wireless LAN communication, this term may be used to signify a STA participating in uplink MU MIMO and/or uplink OFDMA transmission. However, the meaning of this term will not be limited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEE standard.

As illustrated in FIG. 2, various types of PHY protocol data units (PPDUs) may be used in a standard such as IEEE a/g/n/ac, and so on. In detail, LTF and STF fields include a training signal, SIG-A and SIG-B include control information for a receiving station, and a data field includes user data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which is associated with a signal (alternatively, a control information field) used for the data field of the PPDU. The signal provided in the embodiment may be applied onto high efficiency PPDU (HE PPDU) according to an IEEE 802.11ax standard. That is, the signal improved in the embodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. The HE-SIG-A and the HE-SIG-B may be represented even as the SIG-A and SIG-B, respectively. However, the improved signal proposed in the embodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-B standard and may be applied to control/data fields having various names, which include the control information in a wireless communication system transferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be the HE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is one example of the PPDU for multiple users and only the PPDU for the multiple users may include the HE-SIG-B and the corresponding HE SIG-B may be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) may include a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A (HE-SIG A), a high efficiency-signal-B (HE-SIG B), a high efficiency-short training field (HE-STF), a high efficiency-long training field (HE-LTF), a data field (alternatively, an MAC payload), and a packet extension (PE) field. The respective fields may be transmitted during an illustrated time period (that is, 4 or 8/Ls).

More detailed description of the respective fields of FIG. 3 will be made below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) used in a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone (that is, subcarriers) of different numbers are used to constitute some fields of the HE-PPDU. For example, the resources may be allocated by the unit of the RU illustrated for the HE-STF, the HE-LTF, and the data field.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, units corresponding to 26 tones). 6 tones may be used as a guard band in a leftmost band of the 20 MHz band and 5 tones may be used as the guard band in a rightmost band of the 20 MHz band. Further, 7 DC tones may be inserted into a center band, that is, a DC band and a 26-unit corresponding to each 13 tones may be present at left and right sides of the DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated to other bands. Each unit may be allocated for a receiving station, that is, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for a single user (SU) in addition to the multiple users (MUs) and, in this case, as illustrated in a lowermost part of FIG. 4, one 242-unit may be used and, in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a 52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result, since detailed sizes of the RUs may extend or increase, the embodiment is not limited to a detailed size (that is, the number of corresponding tones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) used in a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in one example of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the like, may be used even in one example of FIG. 5. Further, 5 DC tones may be inserted into a center frequency, 12 tones may be used as the guard band in the leftmost band of the 40 MHz band and 11 tones may be used as the guard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used for the single user, the 484-RU may be used. That is, the detailed number of RUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) used in a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in one example of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the like, may be used even in one example of FIG. 6. Further, 7 DC tones may be inserted into the center frequency, 12 tones may be used as the guard band in the leftmost band of the 80 MHz band and 11 tones may be used as the guard band in the rightmost band of the 80 MHz band. In addition, the 26-RU may be used, which uses 13 tones positioned at each of left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for the single user, 996-RU may be used and, in this case, 5 DC tones may be inserted.

Meanwhile, the detailed number of RUs may be modified similarly to one example of each of FIG. 4 or FIG. 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing the HE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF (700) may include a short training orthogonal frequency division multiplexing (OFDM) symbol. The L-STF (700) may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency/time synchronization.

An L-LTF (710) may include a long training orthogonal frequency division multiplexing (OFDM) symbol. The L-LTF (710) may be used for fine frequency/time synchronization and channel prediction.

An L-SIG (720) may be used for transmitting control information. The L-SIG (720) may include information regarding a data rate and a data length. Further, the L-SIG (720) may be repeatedly transmitted. That is, a new format, in which the L-SIG (720) is repeated (for example, may be referred to as R-LSIG) may be configured.

An HE-SIG-A (730) may include the control information common to the receiving station.

In detail, the HE-SIG-A (730) may include information on 1) a DL/UL indicator, 2) a BSS color field indicating an identify of a BSS, 3) a field indicating a remaining time of a current TXOP period, 4) a bandwidth field indicating at least one of 20, 40, 80, 160 and 80+80 MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6) an indication field regarding whether the HE-SIG-B is modulated by a dual subcarrier modulation technique for MCS, 7) a field indicating the number of symbols used for the HE-SIG-B, 8) a field indicating whether the HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) a field indicating the number of symbols of the HE-LTF, 10) a field indicating the length of the HE-LTF and a CP length, 11) a field indicating whether an OFDM symbol is present for LDPC coding, 12) a field indicating control information regarding packet extension (PE), and 13) a field indicating information on a CRC field of the HE-SIG-A, and the like. A detailed field of the HE-SIG-A may be added or partially omitted. Further, some fields of the HE-SIG-A may be partially added or omitted in other environments other than a multi-user (MU) environment.

In addition, the HE-SIG-A (730) may be composed of two parts: HE-SIG-A1 and HE-SIG-A2. HE-SIG-A1 and HE-SIG-A2 included in the HE-SIG-A may be defined by the following format structure (fields) according to the PPDU. First, the HE-SIG-A field of the HE SU PPDU may be defined as follows.

TABLE 1 Two Parts of Number HE-SIG-A Bit Field of bits Description HE-SIG-A1 B0 Format 1 Differentiate an HE SU PPDU and HE ER SU PPDU from an HE TB PPDU:  Set to 1 for an HE SU PPDU and HE ER SU PPDU B1 Beam Change 1 Set to 1 to indicate that the pre-HE modulated fields of the PPDU are spatially mapped differently from the first symbol of the HE-LTF. Equation (28-6), Equation (28-9), Equation (28-12), Equation (28-14), Equation (28-16) and Equation (28-18) apply if the Beam Change field is set to 1. Set to 0 to indicate that the pre-HE modulated fields of the PPDU are spatially mapped the same way as the first symbol of the HE-LTF on each tone. Equation (28- 8), Equation (28-10), Equation (28-13), Equation (28- 15), Equation (28-17) and Equation (28-19) apply if the Beam Change field is set to 0. (#16803) B2 UL/DL 1 Indicates whether the PPDU is sent UL or DL. Set to the value indicated by the TXVECTOR parameter UPLINK_FLAG. B3-B6 MCS 4 For an HE SU PPDU:  Set to n for MCSn, where n = 0, 1, 2, . . . , 11  Values 12-15 are reserved For HE ER SU PPDU with Bandwidth field set to 0 (242-tone RU):  Set to n for MCSn, where n = 0, 1, 2  Values 3-15 are reserved For HE ER SU PPDU with Bandwidth field set to 1 (upper frequency 106-tone RU):  Set to 0 for MCS 0  Values 1-15 are reserved B7 DCM 1 Indicates whether or not DCM is applied to the Data field for the MCS indicated.  If the STBC field is 0, then set to 1 to indicate that  DCM is applied to the Data field. Neither DCM nor  STBC shall be applied if(#15489) both the DCM and  STBC are set to 1.  Set to 0 to indicate that DCM is not applied to the  Data field. NOTE- DCM is applied only to HE-MCSs 0, 1, 3 and 4. DCM is applied only to 1 and 2 spatial streams. DCM is not applied in combination with STBC(#15490). B8-B13 BSS Color 6 The BSS Color field is an identifier of the BSS. Set to the value of the TXVECTOR parameter BSS_- COLOR. B14 Reserved 1 Reserved and set to 1 B15-B18 Spatial Reuse 4 Indicates whether or not spatial reuse is allowed during the transmission of this PPDU(#16804). Set to a value from Table 28-21 (Spatial Reuse field encoding for an HE SU PPDU, HE ER SU PPDU, and HE MU PPDU), see 27.11.6 (SPATIAL_REUSE). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PD-based spa- tial reuse during this PPDU. For the interpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B19-B20 Bandwidth 2 For an HE SU PPDU:  Set to 0 for 20 MHz  Set to 1 for 40 MHz  Set to 2 for 80 MHz  Set to 3 for 160 MHz and 80 + 80 MHz For an HE ER SU PPDU:  Set to 0 for 242-tone RU  Set to 1 for upper frequency 106-tone RU within the  primary 20 MHz  Values 2 and 3 are reserved B21-B22 GI + LTF Size 2 Indicates the GI duration and HE-LTF size.  Set to 0 to indicate a 1 × HE-LTF and 0.8 μs GI  Set to 1 to indicate a 2 × HE-LTF and 0.8 μs GI  Set to 2 to indicate a 2 × HE-LTF and 1.6 μs GI  Set to 3 to indicate:   a 4 × HE-LTF and 0.8 μs GI if both the DCM   and STBC fields are 1. Neither DCM nor   STBC shall be applied if(#Ed) both the DCM   and STBC fields arc set to 1.   a 4 × HE-LTF and 3.2 μs GI, otherwise B23-B25 NSTS And 3 If the Doppler field is 0, indicates the number of space- Midamble time streams. Periodicity  Set to the number of space-time streams minus 1 For an HE ER SU PPDU, values 2 to 7 are reserved If the Doppler field is 1, then B23-B24 indicates the number of space time streams, up to 4, and B25 indi- cates the midamble periodicity. B23-B24 is set to the number of space time streams minus 1. For an HE ER SU PPDU, values 2 and 3 are reserved B25 is set to 0 if TXVECTOR parameter MIDAMBLE_PERIODICITY is 10 and set to 1 if TXVECTOR parameter MIDAMBLE_PERIODICITY is 20. HE-SIG-A2 B0-B6 TXOP 7 Set to 127 to indicate no duration information (HE SU if(#15491) TXVECTOR parameter TXOP_DURA- PPDU)or TION is set to UNSPECIFIED. HE-SIG-A3 Set to a value less than 127 to indicate duration infor- (HE ER SU mation for NAV setting and protection of the TXOP as PPDU) follows:  If TXVECTOR parameter TXOP_DURATION is  less than 512, then B0 is set to 0 and B1-B6 is set to  floor(TXOP_DURATION/8)(#16277).  Otherwise, B0 is set to 1 and B1-B6 is set to floor  ((TXOP_DURATION-512)/128(#16277). where(#16061)  B0 indicates the TXOP length granularity. Set to 0  for 8 μs; otherwise set to 1 for 128 μs.  B1-B6 indicates the scaled value of the  TXOP_DURATION B7 Coding 1 Indicates whether BCC or LDPC is used:  Set to 0 indicate BCC  Set to 1 to indicate LDPC B8 LDPC Extra 1 Indicates the presence of the extra OFDM symbol seg- Symbol ment for LDPC: Segment  Set to 1 if an extra OFDM symbol segment for  LDPC is present  Set to 0 if an extra OFDM symbol segment for  LDPC is not present Reserved and set to 1 if the Coding field is set to 0(#15492). B9 STBC 1 If the DCM field is set to 0, then set to 1 if space time block coding is used. Neither DCM nor STBC shall be applied if(#15493) both the DCM field and STBC field are set to 1. Set to 0 otherwise. B10 Beam- 1 Set to 1 if a beamforming steering matrix is applied to formed(#16038) the waveform in an SU transmission. Set to 0 otherwise. B11-B12 Pre-FEC 2 Indicates the pre-FEC padding factor. Padding Factor Set to 0 to indicate a pre-FEC padding factor of 4 Set to 1 to indicate a pre-FEC padding factor of 1 Set to 2 to indicate a pre-FEC padding factor of 2 Set to 3 to indicate a pre-FEC padding factor of 3 B13 PE Disambi- 1 Indicates PE disambiguity(#16274) as defined in guity 28.3.12 (Packet extension). B14 Reserved 1 Reserved and set to 1 B15 Doppler 1 Set to 1 if one of the following applies:  The number of OFDM symbols in the Data  field is larger than the signaled midamble peri-  odicity plus 1 and the midamble is present  The number of OFDM symbols in tire Data  field is less than or equal to the signaled mid-  amble periodicity plus 1 (see 28.3.11.16 Mid-  amble), the midamble is not present, but the  channel is fast varying. It recommends that  midamble may be used for the PPDUs of the  reverse link. Set to 0 otherwise. B16-B19 CRC 4 CRC for bits 0-41 of the HE-SIG-A field (see 28.3.10.7.3 (CRC computation)). Bits 0-41 of the HE-SIG-A field correspond to bits 0-25 of HE-SIG-A1 followed by bits 0-15 of HE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of the convolutional decoder. Set to 0.

In addition, the HE-SIG-A field of the HE MU PPDU may be defined as follows.

TABLE 2 Two Parts of Number HE-SIG-A Bit Field of bits Description HE-SIG-A1 B0 UL/DL 1 Indicates whether the PPDU is sent UL or DL. Set to the value indicated bv the TXVECTOR parameter UPLINK_FLAG.(#16805) NOTE- The TDLS peer can identify the TDLS frame by To DS and From DS fields in the MAC header of the MPDU. B1-B3 SIGB MCS 3 Indicates the MCS of the HE-SIG-B field:  Set to 0 for MCS 0  Set to 1 for MCS 1  Set to 2 for MCS 2  Set to 3 for MCS 3  Set to 4 for MCS 4  Set to 5 for MCS 5  The values 6 and 7 are reserved B4 SIGB DCM 1 Set to 1 indicates that the HE-SIG-B is modulated with DCM for the MCS. Set to 0 indicates that the HE-SIG-B is not modulated with DCM for the MCS. NOTE- DCM is only applicable to MCS 0, MCS 1, MCS 3, and MCS 4. B5-B10 BSS Color 6 The BSS Color field is an identifier of the BSS. Set to the value of the TXVECTOR parameter BSS_- COLOR. B11-B14 Spatial Reuse 4 Indicates whether or not spatial reuse is allowed during the transmission of this PPDU(#16806). Set to the value of the SPATIAL_REUSE parameter of the TXVECTOR, which contains a value from Table 28-21 (Spatial Reuse field encoding for an HE SU PPDU, HE ER SU PPDU, and HE MU PPDU) (see 27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PD-based spa- tial reuse during this PPDU. For the interpretation of other values sec 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B15-B17 Bandwidth 3 Set to 0 for 20 MHz. Set to 1 for 40 MHz. Set to 2 for 80 MHz Set to 3 for 160 MHz and 80 + 80 MHz non-preamble puncturing mode. If the SIGB Compression field is 0:  Set to 4 for preamble puncturing in 80 MHz, where  in the preamble only the secondary 20 MHz is  punctured.  Set to 5 for preamble puncturing in 80 MHz, where  in the preamble only one of the two 20 MHz sub-  channels in secondary 40 MHz is punctured.  Set to 6 for preamble puncturing in 160 MHz or  80 + 80 MHz, where in the primary 80 MHz of the  preamble only the secondary 20 MHz is punctured.  Set to 7 for preamble puncturing in 160 MHz or  80 + 80 MHz, where in the primary 80 MHz of the  preamble the primary 40 MHz is present. If the SIGB Compression field is 1 then values 4-7 are reserved. B18-B21 Number Of 4 If the HE-SIG-B Compression field is set to 0, HE-SIG-B indicates the number of OFDM symbols in the HE- Symbols Or SIG-B field: (#15494) MU-MIMO  Set to the number of OFDM symbols in the HE-SIG- Users  B field minus 1 if the number of OFDM symbols in  the HE-SIG-B field is less than 16;  Set to 15 to indicate that the number of OFDM sym-  bols in the HE-SIG-B field is equal to 16 if Longer  Than 16 HE SIG-B OFDM Symbols Support sub-  field of the HE Capabilities element transmitted by  at least one recipient STA is 0;  Set to 15 to indicate that the number of OFDM sym-  bols in the HE-SIG-B field is greater than or equal to  16 if the Longer Than 16 HE SIG-B OFDM Sym-  bols Support subfield of the HE Capabilities element  transmitted by all the recipient STAs are 1 and if the  HE-SIG-B data rate is less than MCS 4 without  DCM. The exact number of OFDM symbols in the  HE-SIG-B field is calculated based on the number of  User fields in the HE-SIG-B content channel which  is indicated by HE-SIG-B common field in this case. If the HE-SIG-B Compression field is set lo 1, indicates the number of MU-MIMO users and is set to the num- ber of NU-MIMO users minus (#15495). B22 SIGB 1 Set to 0 if the Common field in HE-SIG-B is present. Compression Set to 1 if the Common field in HE-SIG-B is not present.(#16139) B23-B24 GI + LTF Size 2 Indicates the GI duration and HE-LTF size:  Set to 0 to indicate a 4 × HE-LTF and 0.8 μs GI  Set to 1 to indicate a 2 × HE-LTF and 0.8 μs GI  Set to 2 to indicate a 2 × HE-LTF and 1.6 μs GI  Set to 3 to indicate a 4 × HE-LTF and 3.2 μs GI B25 Doppler 1 Set to 1 if one of the following applies:  The number of OFDM symbols in the Data  field is larger than the signaled midamble peri-  odicity plus 1 and the midamble is present  The number of OFDM symbols in tire Data  field is less than or equal to the signaled mid-  amble periodicity plus 1 (see 28.3.11.16 Mid-  amble), the midamble is not present, but the  channel is fast varying. It recommends that  midamble may be used for the PPDUs of the  reverse link. Set to 0 otherwise. HE-SIG-A2 B0-B6 TXOP 7 Set to 127 to indicate duration information if(#15496) TXVECTOR parameter TXOP_DURATION is set to UNSPECIFIED. Set to a value less than 127 to indicate duration infor- mation for NAV setting and protection of the TXOP as follows:  If TXVECTOR parameter TXOP_DURATION is  less than 512, then B0 is set to 0 and B1-B6 is set to  floor(TXOP_DURATION/8)(#16277).  Otherwise, B0 is set to 1 and B1-B6 is set to floor  ((TXOP_DURATION-512)/128(#16377). where(#16061)  B0 indicates the TXOP length granularity. Set to 0  for 8 μs; otherwise set to 1 for 128 μs.  B1-B6 indicates the scaled value of the  TXOP_DURATION B7 Reserved 1 Reserved and set to 1 B8-B10 Number of 3 If the Doppler field is set to 0(#15497), indicates the HE-LTF number of HE-LTF symbols: Symbols And  Set to 0 for 1 HE-LTF symbol Midamble  Set to 1 for 2 HE-LTF symbols Periodicity  Set to 2 for 4 HE-LTF symbols  Set to 3 for 6 HE-LTF symbols  Set to 4 for 8 HE-LTF symbols  Other values are reserved. If the Doppler field is set to 1(#15498), B8-B9 indi- cates the number of HE-LTF symbols(#16056) and B10 indicates midamble periodicity: B8-B9 is encoded as follows:  0 indicates 1 HE-LTF symbol  1 indicates 2 HE-LTF symbols  2 indicates 4 HE-LTF symbols  3 is reserved B10 is set to 0 if the TXVECTOR parameter MIDAMBLE_PERIODICITY is 10 and set to 1 if the TXVECTOR parameter PREAMBLE_PERIODICITY is 20. B11 LDPC Extra 1 Indication of the presence of the extra OFDM symbol Symbol segment for LDPC. Segment  Set to 1 if an extra OFDM symbol segment for  LDPC is present.  Set to 0 otherwise. B12 STBC 1 In an HE MU PPDU where each RU includes no more than 1 user, set to 1 to indicate all RUs are STBC encoded in the payload, set to 0 to indicate all RUs are not STBC encoded in the payload. STBC does not apply to HE-SIG-B. STBC is not applied if one or more RUs are used for MU-MIMO allocation. (#15661) B13-B14 Pre-FEC 2 Indicates the pre-FEC padding factor. Padding Set to 0 to indicate a pre-FEC padding factor of 4 Factor Set to 1 to indicate a pre-FEC padding factor of 1 Set to 2 to indicate a pre-FEC padding factor of 2 Set to 3 to indicate a pre-FEC padding factor of 3 B15 PE 1 Indicates PE disambiguity(#16274) as defined in Disambiguity 28.3.12 (Packet extension). B16-B19 CRC 4 CRC for bits 0-41 of the HE-SIG-A field (see 28.3.10.7.3 (CRC computation)). Bits 0-41 of the HE-SIG-A field correspond to bits 0-25 of HE-SIG-A1 followed by bits 0-15 of HE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of the convolutional decoder. Set to 0.

In addition, the HE-SIG-A field of the HE TB PPDU may be defined as follows.

TABLE 3 Two Parts of Number HE-SIG-A Bit Field of bits Description HE-SIG-A1 B0 Format 1 Differentiate an HE SU PPDU and HE ER SU PPDU from an HE TB PPDU:  Set to 0 for an HE TB PPDU B1-B6 BSS Color 6 The BSS Color field is an identifier of the BSS. Set to the value of the TXVECTOR parameter BSS_- COLOR. B7-B10 Spatial Reuse 1 4 Indicates whether or not spatial reuse is allowed in a subband of the PPDU during the transmission of this PPDU, and if allowed, indicates a value that is used to determine a limit on the transmit power of a spatial reuse transmission. If the Bandwidth field indicates 20 MHz, 40 MHz, or 80 MHz then this Spatial Reuse field applies to the first 20 MHz subband. If the Bandwidth field indicates 160/80 + 80 MHz then this Spatial Reuse field applies to the first 40 MHz sub- band of the 160 MHz operating band. Set to the value of the SPATIAL_REUSE(1) parameter of the TXVECTOR, which contains a value from Table 28-22 (Spatial Reuse field encoding for an HE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PD-based spa- tial reuse during this PPDU. For the interpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B11-B14 Spatial Reuse 2 4 Indicates whether or not spatial reuse is allowed in a subband of the PPDU during the transmission of this PPDU, and if allowed, indicates a value that is used to determine a limit on the transmit power of a spatial reuse transmission. If the Bandwidth field indicates 20 MHz, 40 MHz, or 80 MHz:  This Spatial Reuse field applies to the second  20 MHz subband.  If(#Ed) the STA operating channel width is 20 MHz,  then this field is set to the same value as Spatial  Reuse 1 field.  If(#Ed) the STA operating channel width is 40 MHz  in the 2.4 GHz band, this field is set to the same  value as Spatial Reuse 1 field. If the Bandwidth field indicates 160/80 + 80 MHz the this Spatial Reuse field applies to the second 40 MHz subband of the 160 MHz operating band. Set to the value of the SPATIAL_REUSE(2) parameter of the TXVECTOR, which contains a value from Table 28-22 (Spatial Reuse field encoding for an HE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PD-based spa- tial reuse during this PPDU. For the interpretation of other values sec 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B15-B18 Spatial Reuse 3 4 Indicates whether or not spatial reuse is allowed in a subband of the PPDU during the transmission of this PPDU, and if allowed, indicates a value that is used to determine a limit on the transmit power of a spatial reuse transmission. If the Bandwidth field indicates 20 MHz, 40 MHz or 80 MHz:  This Spatial Reuse field applies to the third 20 MHz  subband.  If(#Ed) the STA operating channel width is 20 MHz  or 40 MHz, this field is set to the same value as  Spatial Reuse 1 field. If the Bandwidth field indicates 160/80 + 80 MHz:  This Spatial Reuse field applies to the third 40 MHz  subband of the 160 MHz operating band.  If(#Ed) the STA operating channel width is  80 + 80 MHz, this field is set to the same value as  Spatial Reuse 1 field. Set to the value of the SPATIAL_REFUSE(3) parameter of the TXVECTOR, which contains a value from Table 28-22 (Spatial Reuse field encoding for an HE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse daring this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PD-based spatial reuse during this PPDU. For the interpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B19-B22 Spatial Reuse 4 4 Indicates whether or not spatial reuse is allowed in a subband of the PPDU during the transmission of this PPDU, and if allowed, indicates a value that is used to determine a limit on the transmit power of a spatial reuse transmission. If the Bandwidth field indicates 20 MHz, 40 MHz or 80 MHz:  This Spatial Reuse field applies to the fourth 20  MHz subband.  If(#Ed) the STA operating channel width is 20 MHz,  then this field is set to the same value as Spatial  Reuse 1 field.  If(#Ed) the STA operating channel width is 40 MHz,  then this field is set to the same value as Spatial  Reuse 2 field. If the Bandwidth field indicates 160/80 + 80 MHz: This Spatial Reuse field applies to the fourth 40 MHz subband of the 160 MHz operating band. If(#Ed) the STA operating channel width is 80 + 80 MHz, then this field is set to same value as Spatial Reuse 2 field. Set to the value of the SPATIAL_REUSE(4) parameter of the TXVECTOR, which contains a value from Table 28-22 (Spatial Reuse field encoding for an HE TB PPDU) for an HE TB PPDU (see 27.11.6 (SPATIAL_REUSE)). Set to SRP_DISALLOW to prohibit SRP-based spatial reuse during this PPDU. Set to SRP_AND_NON_S- RG_OBSS_PD_PROHIBITED to prohibit both SRP- based spatial reuse and non-SRG OBSS PI)-based spatial reuse during this PPDU. For the interpretation of other values see 27.11.6 (SPATIAL_REUSE) and 27.9 (Spatial reuse operation). B23 Reserved 1 Reserved and set to 1. NOTE- Unlike other Reserved fields in HE-SIG-A of the HE TB PPDU, B23 does not have a corresponding bit in the Trigger frame. B24-B25 Bandwidth 2 (#16003)Set to 0 for 20 MHz Set to 1 for 40 MHz Set to 2 for 80 MHz Set to 3 for 160 MHz and 80 + 80 MHz HE-SIG-A2 B0-B6 TXOP 7 Set to 127 to indicate no duration information if(#15499) TXVECTOR parameter TXOP_DURATION is set to UNSPECIFIED. Set to a value less than 127 to indicate duration infor- mation for NAV setting and protection of the TXOP as follows:  If TXVECTOR parameter TXOP_DURATION is  less than 512, then B0 is set to 0 and B1-B6 is set to  floor(TXOP_DURATION/8)(#16277).  Otherwise, B0 is set to 1 and B1-B6 is set to floor  ((TXOP_DURATION-512)/128)(#16277). where(#16061)  B0 indicates the TXOP length granularity. Set to 0  for 8 μs; otherwise set to 1 for 128 μs.  B1-B6 indicates the scaled value of the  TXOP_DURATION B7-B15 Reserved 9 Reserved and set to value indicated in the UL HE-SIG- A2 Reserved subfield in the Trigger frame. B16-B19 CRC 4 CRC of bits 0-41 of the HE-SIG-A field. See 28.3.10.7.3 (CRC computation). Bits 0-41 of the HE-SIG-A field correspond to bits 0-25 of HE-SIG-A1 followed by bits 0-15 of HE-SIG-A2). B20-B25 Tail 6 Used to terminate the trellis of the convolutional decoder. Set to 0.

An HE-SIG-B (740) may be included only in the case of the PPDU for the multiple users (MUs) as described above. Principally, an HE-SIG-A (750) or an HE-SIG-B (760) may include resource allocation information (alternatively, virtual resource allocation information) for at least one receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B according to an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field at a frontmost part and the corresponding common field is separated from a field which follows therebehind to be encoded. That is, as illustrated in FIG. 8, the HE-SIG-B field may include a common field including the common control information and a user-specific field including user-specific control information. In this case, the common field may include a CRC field corresponding to the common field, and the like and may be coded to be one BCC block. The user-specific field subsequent thereafter may be coded to be one BCC block including the “user-specific field” for 2 users and a CRC field corresponding thereto as illustrated in FIG. 8.

A previous field of the HE-SIG-B (740) may be transmitted in a duplicated form on a MU PPDU. In the case of the HE-SIG-B (740), the HE-SIG-B (740) transmitted in some frequency band (e.g., a fourth frequency band) may even include control information for a data field corresponding to a corresponding frequency band (that is, the fourth frequency band) and a data field of another frequency band (e.g., a second frequency band) other than the corresponding frequency band. Further, a format may be provided, in which the HE-SIG-B (740) in a specific frequency band (e.g., the second frequency band) is duplicated with the HE-SIG-B (740) of another frequency band (e.g., the fourth frequency band). Alternatively, the HE-SIG B (740) may be transmitted in an encoded form on all transmission resources. A field after the HE-SIG B (740) may include individual information for respective receiving STAs receiving the PPDU.

The HE-STF (750) may be used for improving automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment.

The HE-LTF (760) may be used for estimating a channel in the MIMO environment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT) applied to the HE-STF (750) and the field after the HE-STF (750), and the size of the FFT/IFFT applied to the field before the HE-STF (750) may be different from each other. For example, the size of the FFT/IFFT applied to the HE-STF (750) and the field after the HE-STF (750) may be four times larger than the size of the FFT/IFFT applied to the field before the HE-STF (750).

For example, when at least one field of the L-STF (700), the L-LTF (710), the L-SIG (720), the HE-SIG-A (730), and the HE-SIG-B (740) on the PPDU of FIG. 7 is referred to as a first field, at least one of the data field (770), the HE-STF (750), and the HE-LTF (760) may be referred to as a second field. The first field may include a field associated with a legacy system and the second field may include a field associated with an HE system. In this case, the fast Fourier transform (FFT) size and the inverse fast Fourier transform (IFFT) size may be defined as a size which is N (N is a natural number, e.g., N=1, 2, and 4) times larger than the FFT/IFFT size used in the legacy wireless LAN system. That is, the FFT/IFFT having the size may be applied, which is N(=4) times larger than the first field of the HE PPDU. For example, 256 FFT/IFFT may be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied to a bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80 MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160 MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a size which is 1/N times (N is the natural number, e.g., N=4, the subcarrier spacing is set to 78.125 kHz) the subcarrier space used in the legacy wireless LAN system. That is, subcarrier spacing having a size of 312.5 kHz, which is legacy subcarrier spacing may be applied to the first field of the HE PPDU and a subcarrier space having a size of 78.125 kHz may be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the first field may be expressed to be N(=4) times shorter than the IDFT/DFT period applied to each data symbol of the second field. That is, the IDFT/DFT length applied to each symbol of the first field of the HE PPDU may be expressed as 3.2 us and the IDFT/DFT length applied to each symbol of the second field of the HE PPDU may be expressed as 3.2 μs*4 (=12.8 μs). The length of the OFDM symbol may be a value acquired by adding the length of a guard interval (GI) to the IDFT/DFT length. The length of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs, 2.4 μs, and 3.2 μs.

For simplicity in the description, in FIG. 7, it is expressed that a frequency band used by the first field and a frequency band used by the second field accurately coincide with each other, but both frequency bands may not completely coincide with each other, in actual. For example, a primary band of the first field (L-STF, L-LTF, L-SIG, HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may be the same as the most portions of a frequency band of the second field (HE-STF, HE-LTF, and Data), but boundary surfaces of the respective frequency bands may not coincide with each other. As illustrated in FIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones, and the like are inserted during arranging the RUs, it may be difficult to accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A (730) and may be instructed to receive the downlink PPDU based on the HE-SIG-A (730). In this case, the STA may perform decoding based on the FFT size changed from the HE-STF (750) and the field after the HE-STF (750). On the contrary, when the STA may not be instructed to receive the downlink PPDU based on the HE-SIG-A (730), the STA may stop the decoding and configure a network allocation vector (NAV). A cyclic prefix (CP) of the HE-STF (750) may have a larger size than the CP of another field and the during the CP period, the STA may perform the decoding for the downlink PPDU by changing the FFT size.

Hereinafter, in the embodiment of the present disclosure, data (alternatively, or a frame) which the AP transmits to the STA may be expressed as a terms called downlink data (alternatively, a downlink frame) and data (alternatively, a frame) which the STA transmits to the AP may be expressed as a term called uplink data (alternatively, an uplink frame). Further, transmission from the AP to the STA may be expressed as downlink transmission and transmission from the STA to the AP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and data transmitted through the downlink transmission may be expressed as terms such as a downlink PPDU, a downlink frame, and downlink data, respectively. The PPDU may be a data unit including a PPDU header and a physical layer service data unit (PSDU) (alternatively, a MAC protocol data unit (MPDU)). The PPDU header may include a PHY header and a PHY preamble and the PSDU (alternatively, MPDU) may include the frame or indicate the frame (alternatively, an information unit of the MAC layer) or be a data unit indicating the frame. The PHY header may be expressed as a physical layer convergence protocol (PLCP) header as another term and the PHY preamble may be expressed as a PLCP preamble as another term.

Further, a PPDU, a frame, and data transmitted through the uplink transmission may be expressed as terms such as an uplink PPDU, an uplink frame, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the present description is applied, the total bandwidth may be used for downlink transmission to one STA and uplink transmission to one STA. Further, in the wireless LAN system to which the embodiment of the present description is applied, the AP may perform downlink (DL) multi-user (MU) transmission based on multiple input multiple output (MU MIMO) and the transmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, an orthogonal frequency division multiple access (OFDMA) based transmission method is preferably supported for the uplink transmission and/or downlink transmission. That is, data units (e.g., RUs) corresponding to different frequency resources are allocated to the user to perform uplink/downlink communication. In detail, in the wireless LAN system according to the embodiment, the AP may perform the DL MU transmission based on the OFDMA and the transmission may be expressed as a term called DL MU OFDMA transmission. When the DL MU OFDMA transmission is performed, the AP may transmit the downlink data (alternatively, the downlink frame and the downlink PPDU) to the plurality of respective STAs through the plurality of respective frequency resources on an overlapped time resource. The plurality of frequency resources may be a plurality of subbands (alternatively, subchannels) or a plurality of resource units (RUs). The DL MU OFDMA transmission may be used together with the DL MU MIMO transmission. For example, the DL MU MIMO transmission based on a plurality of space-time streams (alternatively, spatial streams) may be performed on a specific subband (alternatively, subchannel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplink multi-user (UL MU) transmission in which the plurality of STAs transmits data to the AP on the same time resource may be supported. Uplink transmission on the overlapped time resource by the plurality of respective STAs may be performed on a frequency domain or a spatial domain.

When the uplink transmission by the plurality of respective STAs is performed on the frequency domain, different frequency resources may be allocated to the plurality of respective STAs as uplink transmission resources based on the OFDMA. The different frequency resources may be different subbands (alternatively, subchannels) or different resources units (RUs). The plurality of respective STAs may transmit uplink data to the AP through different frequency resources. The transmission method through the different frequency resources may be expressed as a term called a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs is performed on the spatial domain, different time-space streams (alternatively, spatial streams) may be allocated to the plurality of respective STAs and the plurality of respective STAs may transmit the uplink data to the AP through the different time-space streams. The transmission method through the different spatial streams may be expressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be used together with each other. For example, the UL MU MIMO transmission based on the plurality of space-time streams (alternatively, spatial streams) may be performed on a specific subband (alternatively, subchannel) allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMA transmission, a multi-channel allocation method is used for allocating a wider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. When a channel unit is 20 MHz, multiple channels may include a plurality of 20 MHz-channels. In the multi-channel allocation method, a primary channel rule is used to allocate the wider bandwidth to the terminal. When the primary channel rule is used, there is a limit for allocating the wider bandwidth to the terminal. In detail, according to the primary channel rule, when a secondary channel adjacent to a primary channel is used in an overlapped BSS (OBSS) and is thus busy, the STA may use remaining channels other than the primary channel. Therefore, since the STA may transmit the frame only to the primary channel, the STA receives a limit for transmission of the frame through the multiple channels. That is, in the legacy wireless LAN system, the primary channel rule used for allocating the multiple channels may be a large limit in obtaining a high throughput by operating the wider bandwidth in a current wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN system is disclosed, which supports the OFDMA technology. That is, the OFDMA technique may be applied to at least one of downlink and uplink. Further, the MU-MIMO technique may be additionally applied to at least one of downlink and uplink. When the OFDMA technique is used, the multiple channels may be simultaneously used by not one terminal but multiple terminals without the limit by the primary channel rule. Therefore, the wider bandwidth may be operated to improve efficiency of operating a wireless resource.

As described above, in case the uplink transmission performed by each of the multiple STAs (e.g., non-AP STAs) is performed within the frequency domain, the AP may allocate different frequency resources respective to each of the multiple STAs as uplink transmission resources based on OFDMA. Additionally, as described above, the frequency resources each being different from one another may correspond to different subbands (or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multiple STAs are indicated through a trigger frame.

FIG. 9 illustrates an example of a trigger frame. The trigger frame of FIG. 9 allocates resources for Uplink Multiple-User (MU) transmission and may be transmitted from the AP. The trigger frame may be configured as a MAC frame and may be included in the PPDU. For example, the trigger frame may be transmitted through the PPDU shown in FIG. 3, through the legacy PPDU shown in FIG. 2, or through a certain PPDU, which is newly designed for the corresponding trigger frame. In case the trigger frame is transmitted through the PPDU of FIG. 3, the trigger frame may be included in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or other fields may be added. Moreover, the length of each field may be varied differently as shown in the drawing.

A Frame Control field (910) shown in FIG. 9 may include information related to a version of the MAC protocol and other additional control information, and a Duration field (920) may include time information for configuring a NAV or information related to an identifier (e.g., AID) of the user equipment.

Also, the RA field (930) includes address information of a receiving STA of the corresponding trigger frame and may be omitted if necessary. The TA field (940) includes address information of an STA triggering the corresponding trigger frame (for example, an AP), and the common information field (950) includes common control information applied to a receiving STA that receives the corresponding trigger frame. For example, a field indicating the length of the L-SIG field of the UL PPDU transmitted in response to the corresponding trigger frame or information controlling the content of the SIG-A field (namely, the HE-SIG-A field) of the UL PPDU transmitted in response to the corresponding trigger frame may be included. Also, as common control information, information on the length of the CP of the UP PPDU transmitted in response to the corresponding trigger frame or information on the length of the LTF field may be included.

Also, it is preferable to include a per user information field (960 #1 to 960 #N) corresponding to the number of receiving STAs that receive the trigger frame of FIG. 9. The per user information field may be referred to as an “RU allocation field”.

Also, the trigger frame of FIG. 9 may include a padding field (970) and a frame check sequence field (980).

It is preferable that each of the per user information fields (960 #1 to 960 #N) shown in FIG. 9 includes a plurality of subfields.

FIG. 10 illustrates an example of a common information field. Among the subfields of FIG. 10, some may be omitted, and other additional subfields may also be added. Additionally, the length of each of the subfields shown in the drawing may be varied.

The trigger type field (1010) of FIG. 10 may indicate a trigger frame variant and encoding of the trigger frame variant. The trigger type field (1010) may be defined as follows.

TABLE 4   Trigger Type subfield value Trigger frame variant 0 Basic 1 Beamforming Report Poll (BFRP) 2 MU-BAR 3 MU-RTS 4 Buffer Status Report Poll (BSRP) 5 GCR MU-BAR 6 Bandwidth Query Report Poll (BQRP) 7 NDP Feedback Report Poll (NFRP) 8-15 Reserved

The UL BW field (1020) of FIG. 10 indicates bandwidth in the HE-SIG-A field of an HE Trigger Based (TB) PPDU. The UL BW field (1020) may be defined as follows.

TABLE 5   UL BW subfield value Description 0 20 MHz 1 40 MHz 2 80 MHz 3 80 + 80 MHz or 160 MHz

The Guard Interval (GI) and LTF type fields (1030) of FIG. 10 indicate the GI and HE-LTF type of the HE TB PPDU response. The GI and LTF type field (1030) may be defined as follows.

TABLE 6   GI And LTF field value Description 0 1 × HE-LTF + 1.6 μs GI 1 2 × HE-LTF + 1.6 μs GI 2 4 × HE-LTF + 3.22 μs GI(#15968) 3 Reserved

Also, when the GI and LTF type fields (1030) have a value of 2 or 3, the MU-MIMO LTF mode field (1040) of FIG. 10 indicates the LTF mode of a UL MU-MIMO HE TB PPDU response. At this time, the MU-MIMO LTF mode field (1040) may be defined as follows.

If the trigger frame allocates an RU that occupies the whole HE TB PPDU bandwidth and the RU is allocated to one or more STAs, the MU-MIMO LTF mode field (1040) indicates one of an HE single stream pilot HE-LTF mode or an HE masked HE-LTF sequence mode.

If the trigger frame does not allocate an RU that occupies the whole HE TB PPDU bandwidth and the RU is not allocated to one or more STAs, the MU-MIMO LTF mode field (1040) indicates the HE single stream pilot HE-LTF mode. The MU-MIMO LTF mode field (1040) may be defined as follows.

TABLE 7   MU-MIMO LTF subfield value Description 0 HE single stream pilot HE-LTF mode 1 HE masked HE-LTF sequence mode

FIG. 11 illustrates an example of a subfield being included in a per user information field. Among the subfields of FIG. 11, some may be omitted, and other additional subfields may also be added. Additionally, the length of each of the subfields shown in the drawing may be varied.

The User Identifier field of FIG. 11 (or AID12 field, 1110) indicates the identifier of an STA (namely, a receiving STA) corresponding to per user information, where an example of the identifier may be the whole or part of the AID.

Also, an RU Allocation field (1120) may be included. In other words, when a receiving STA identified by the User Identifier field (1110) transmits a UL PPDU in response to the trigger frame of FIG. 9, the corresponding UL PPDU is transmitted through an RU indicated by the RU Allocation field (1120). In this case, it is preferable that the RU indicated by the RU Allocation field (1120) indicates the RUs shown in FIGS. 4, 5, and 6. A specific structure of the RU Allocation field (1120) will be described later.

The subfield of FIG. 11 may include a (UL FEC) coding type field (1130). The coding type field (1130) may indicate the coding type of an uplink PPDU transmitted in response to the trigger frame of FIG. 9. For example, when BCC coding is applied to the uplink PPDU, the coding type field (1130) may be set to ‘1’, and when LDPC coding is applied, the coding type field (1130) may be set to ‘0’.

Additionally, the subfield of FIG. 11 may include a UL MCS field (1140). The MCS field (1140) may indicate an MCS scheme being applied to the uplink PPDU that is transmitted in response to the trigger frame of FIG. 9.

Also, the subfield of FIG. 11 may include a Trigger Dependent User Info field (1150). When the Trigger Type field (1010) of FIG. 10 indicates a basic trigger variant, the Trigger Dependent User Info field (1150) may include an MPDU MU Spacing Factor subfield (2 bits), a TID Aggregate Limit subfield (3 bits), a Reserved field (1 bit), and a Preferred AC subfield (2 bits).

Hereinafter, the present disclosure proposes an example of improving a control field included in a PPDU. The control field improved according to the present disclosure includes a first control field including control information required to interpret the PPDU and a second control field including control information for demodulate the data field of the PPDU. The first and second control fields may be used for various fields. For example, the first control field may be the HE-SIG-A (730) of FIG. 7, and the second control field may be the HE-SIG-B (740) shown in FIGS. 7 and 8.

Hereinafter, a specific example of improving the first or the second control field will be described.

In the following example, a control identifier inserted to the first control field or a second control field is proposed. The size of the control identifier may vary, which, for example, may be implemented with 1-bit information.

The control identifier (for example, a 1-bit identifier) may indicate whether a 242-type RU is allocated when, for example, 20 MHz transmission is performed. As shown in FIGS. 4 to 6, RUs of various sizes may be used. These RUs may be divided broadly into two types. For example, all of the RUs shown in FIGS. 4 to 6 may be classified into 26-type RUs and 242-type RUs. For example, a 26-type RU may include a 26-RU, a 52-RU, and a 106-RU while a 242-type RU may include a 242-RU, a 484-RU, and a larger RU.

The control identifier (for example, a 1-bit identifier) may indicate that a 242-type RU has been used. In other words, the control identifier may indicate that a 242-RU, a 484-RU, or a 996-RU is included. If the transmission frequency band in which a PPDU is transmitted has a bandwidth of 20 MHz, a 242-RU is a single RU corresponding to the full bandwidth of the transmission frequency band (namely, 20 MHz). Accordingly, the control identifier (for example, 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth of the transmission frequency band is allocated.

For example, if the transmission frequency band has a bandwidth of 40 MHz, the control identifier (for example, a 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth (namely, bandwidth of 40 MHz) of the transmission frequency band has been allocated. In other words, the control identifier may indicate whether a 484-RU has been allocated for transmission in the frequency band with a bandwidth of 40 MHz.

For example, if the transmission frequency band has a bandwidth of 80 MHz, the control identifier (for example, a 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth (namely, bandwidth of 80 MHz) of the transmission frequency band has been allocated. In other words, the control identifier may indicate whether a 996-RU has been allocated for transmission in the frequency band with a bandwidth of 80 MHz.

Various technical effects may be achieved through the control identifier (for example, 1-bit identifier).

First of all, when a single RU corresponding to the full bandwidth of the transmission frequency band is allocated through the control identifier (for example, a 1-bit identifier), allocation information of the RU may be omitted. In other words, since only one RU rather than a plurality of RUs is allocated over the whole transmission frequency band, allocation information of the RU may be omitted deliberately.

Also, the control identifier may be used as signaling for full bandwidth MU-MIMO. For example, when a single RU is allocated over the full bandwidth of the transmission frequency band, multiple users may be allocated to the corresponding single RU. In other words, even though signals for each user are not distinctive in the temporal and spatial domains, other techniques (for example, spatial multiplexing) may be used to multiplex the signals for multiple users in the same, single RU. Accordingly, the control identifier (for example, a 1-bit identifier) may also be used to indicate whether to use the full bandwidth MU-MIMO described above.

The common field included in the second control field (HE-SIG-B, 740) may include an RU allocation subfield. According to the PPDU bandwidth, the common field may include a plurality of RU allocation subfields (including N RU allocation subfields). The format of the common field may be defined as follows.

TABLE 8 Num- ber Subfield of bits Description RU N × 8 Indicates the RU assignment to be used M the data Allocation portion in the frequency domain. It also indicates the number of users in each RU. For RUs of size greater than or equal to 106-tones that support MU-MIMO, it indicates the number of users multiplexed using MU-MIMO. Consists of N RU Allocation subfields:  N = 1 for a 20 MHz and a 40 MHz HE MU  PPDU  N = 2 for an 80 MHz HE MU PPDU  N = 4 for a 160 MHz or 80 + 80 MHz HE MU  PPDU Center 1 This field is present only if(#15510) the value of 26-tone the Bandwidth field of HE-SIG-A field in an HE RU MU PPDU is set to greater than 1. If the Bandwidth field of the HE-SIG-A field in all HE MU PPDU is set to 2, 4 or 5 for 80 MHz:  Set to 1 to indicate that a user is allocated to the  center 26-tone RU (see Figure 28-7 (RU  locations in an 80 MHz HE PPDU(#16528)));  otherwise, set to 0. The same value is applied to  both HE-SIG-B content channels. If the Bandwidth field of the HE-SIG-A field in an HE MU PPDU is set to 3, 6 or 7 for 160 MHz or 80 + 80 MHz:  For HE-SIG-B content channel 1, set to 1 to  indicate that a user is allocated to the center 26-  tone RU of the lower frequency 80 MHz;  otherwise, set to 0.  For HE-SIG-B content channel 2, set to 1 to  indicate that a user is allocated to the center 26-  tone RU of the higher frequency 80 MHz;  otherwise, set to 0. CRC 4 See 28.3.10.7.3 (CRC computation) Tail 6 Used to terminate the trellis of the convolutional decoder. Set to 0

The RU allocation subfield included in the common field of the HE-SIG-B may be configured with 8 bits and may indicate as follows with respect to 20 MHz PPDU bandwidth. RUs to be used as a data portion in the frequency domain are allocated using an index for RU size and disposition in the frequency domain. The mapping between an 8-bit RU allocation subfield for RU allocation and the number of users per RU may be defined as follows.

TABLE 9 8 bits indices (B7 B6 B5 B4 Number B3 B2 B1 B0) #1 #2 #3 #4 #5 #6 #7 #8 #9 of entries 00000000 26 26 26 26 26 26 26 26 26 1 00000001 26 26 26 26 26 26 26 52 1 00000010 26 26 26 26 26 52 26 26 1 00000011 26 26 26 26 26 52 52 1 00000100 26 26 52 26 26 26 26 26 1 00000101 26 26 52 26 26 26 52 1 00000110 26 26 52 26 52 26 26 1 00000111 26 26 52 26 52 52 1 00001000 52 26 26 26 26 26 26 26 1 00001001 52 26 26 26 26 26 52 1 00001010 52 26 26 26 52 26 26 1 00001011 52 26 26 26 52 52 1 00001100 52 52 26 26 26 26 26 1 00001101 52 52 26 26 26 52 1 00001110 52 52 26 52 26 26 1 00001111 52 52 26 52 52 1 00010y₂y₁y₀ 52 52 — 106 8 00011y₂y₁y₀ 106 — 52 52 8 00100y₂y₁y₀ 26 26 26 26 26 106 8 00101y₂y₁y₀ 26 26 52 26 106 8 00110y₂y₁y₀ 52 26 26 26 106 8 00111y₂y₁y₀ 52 52 26 106 8 01000y₂y₁y₀ 106 26 26 26 26 26 8 01001y₂y₁y₀ 106 26 26 26 52 8 01010y₂y₁y₀ 106 26 52 26 26 8 01011y₂y₁y₀ 106 26 52 52 8 0110y₁y₀z₁z₀ 106 — 106 16  01110000 52 52 — 52 52 1 01110001 242-tone RU empty 1 01110010 484-tone RU with zero User fields indicated in this RU 1 Allocation subfield of the HE-SIG-B content channel 01110011 996-tone RU with zero User fields indicated in this RU 1 Allocation subfield of the HE-SIG-B content channel 011101x₁x₀ Reserved 4 01111y₂y₁y₀ Reserved 8 10y₂y₁y₀z₂z₁z₀ 106 26 106 64  11000y₂y₁y₀ 242  8 11001y₂y₁y₀ 484  8 11010y₂y₁y₀ 996  8 11011y₂y₁y₀ Reserved 8 111x₄x₃x₂x₁x₀ Reserved 32   

  signaling RUs of size greater than 242 subcarriers, y₂y₁y₀ = 000-111 indicates number of User fields in the HE-SIG-B content channel that contains the corresponding 8-bit RU Allocation subfield. Otherwise, y₂y₁y₀ = 000-111 indicates, number of STAs multiplexed in the 106-tone RU, 242-tone RU or the lower frequency 106-tone RU if there are two 106-tone RUs and one 26-tone RU is assigned between two 106-tone RUs. The binary vector y₂y₁y₀ indicates 2² × y₂ +2¹ × y₁ + y₀ + 1 STAs multiplexed the RU. z₂z₁z₀ = 000-111 indicates number of STAs multiplexed in the higher frequency 106-tone RU if there are two 106-tone RUs and one 26-tone RU is assigned between two 106-tone RUs. The binary vector z₂z₁z₀ indicates 2² × z₂ +2¹ × z₁ + z₀ + 1 STAs multiplexed the RU. Similarly, y₁y₀ = 00-11 indicates number of STAs multiplexed in the lower frequency 106-tone RU. The binary vector y₁y₀ indicates 2¹ × y₁ + y₀ + 1 STAs multiplexed the RU. Similarly, z₁z₀ = 00-11 indicates number of STAs multiplexed in the higher frequency 106-tone RU. The binary vector z₁z₀ indicates 2¹ × z₁ + z₀ + 1 STAs multiplexed the RU. #1 to #9 (from left to the right) is ordered in increased order of the absolute frequency. x₁x₀ = 00-11, x₄x₃x₂x₁x₀ = 00000-11111.  

  means no STA in that RU.

indicates data missing or illegible when filed

The user-specific field included in the second control field (HE-SIG-B, 740) may include a user field, a CRC field, and a Tail field. The format of the user-specific field may be defined as follows.

TABLE 10 Number Subfield of bits Description User field N × 21 The User field format for a non-MU-MIMO allocation is defined in Table 28-26 (User field format for a non-MU-MIMO allocation). The User field format for a MU-MIMO allocation is defined in Table 28-27 (User field for an MU-MIMO allocation). N = 1 if it is the last User Block field, and if there is only one user in the last User Block field. N = 2 otherwise. CRC 4 The CRC is calculated over bits 0 to 20 for a User Block field that contains one User field, and bits 0 to 41 for a User Block field that contains two User fields. See 28.3.10.7.3 (CRC computation). Tail 6 Used to terminate the trellis of the convolutional decoder. Set to 0.

Also, the user-specific field of the HE-SIG-B is composed of a plurality of user fields. The plurality of user fields are located after the common field of the HE-SIG-B. The location of the RU allocation subfield of the common field and that of the user field of the user-specific field are used together to identify an RU used for transmitting data of an STA. A plurality of RUs designated as a single STA are now allowed in the user-specific field. Therefore, signaling that allows an STA to decode its own data is transmitted only in one user field.

As an example, it may be assumed that the RU allocation subfield is configured with 8 bits of 01000010 to indicate that five 26-tone RUs are arranged next to one 106-tone RU and three user fields are included in the 106-tone RU. At this time, the 106-tone RU may support multiplexing of the three users. This example may indicate that eight user fields included in the user-specific field are mapped to six RUs, the first three user fields are allocated according to the MU-MIMO scheme in the first 106-tone RU, and the remaining five user fields are allocated to each of the five 26-tone RUs.

User fields included in the user-specific field of the HE-SIG-B may be defined as described below. Firstly, user fields for non-MU-MIMO allocation are as described below.

TABLE 12 Number Bit Subfield of bits Description B0- STA-ID 11 Set to a value of the element indicated B10 from TXVECTOR parameter STA_ID_LIST (sec 27.11.1 (STA_ID_LIST)). B11- NSTS  3 Number of space-time streams. B13 Set to the number of space-time streams minus 1. B14 Beam-  1 Use of transmit beamforming. formed(#16038) Set to 1 if a beamforming steering matrix is applied to the waveform in an SU transmission. Set to 0 otherwise. B15- MCS  4 Modulation and coding scheme B18 Set to n for MCSn, where n = 0, 1, 2 . . . , 11 Values 12 to 15 are reserved B19 DCM  1 Indicates whether or not DCM is used.  Set to 1 to indicate that the  payload(#Ed) of the corresponding  user of the HE MU PPDU is  modulated with DCM for the MCS.  Set to 0 to indicate that the payload  of the corresponding user of the  PPDU is not modulated with DCM  for the MCS. NOTE- DCM is not applied in combination with STBC.(#15664) B20 Coding  1 Indicates whether BCC or LDPC is used.  Set to 0 for BCC  Set to 1 for LDPC NOTE- If the STA-ID subfield is set to 2046, then the other subfields can be set to arbitrary values.(#15946)

User fields for MU-MIMO allocation are as described below.

TABLE 13 Number Bit Subfield of bits Description B0- STA-ID 11 Set to a value of element indicated from B10 TXVECTOR parameter STA_ID_LIST (see 27.11.1 (STA_ID_LIST)). B11- Spatial  4 Indicates the number of spatial streams for a B14 Con- STA in an MU-MIMO allocation (see Table figuration 28-28 (Spatial Configuration subfield encoding)). B15- MCS  4 Modulation and coding scheme. B18 Set to n for MCSn, where n = 0, 1, 2, . . . , 11 Values 12 to 15 are reserved B19 Reserved  1 Reserved and set to 0 B20 Coding  1 Indicates whether BCC or LDPC is used.  Set to 0 for BCC  Set to 1 for LDPC NOTE- If the STA-ID subfield is set to 2046, then the other subfields can be set to arbitrary values.(#15946)

FIG. 12 illustrates an example of an HE TB PPDU. The PPDU of FIG. 12 illustrates an uplink PPDU transmitted in response to the trigger frame of FIG. 9. At least one STA receiving a trigger frame from an AP may check the common information field and the individual user information field of the trigger frame and may transmit a HE TB PPDU simultaneously with another STA which has received the trigger frame.

As shown in the figure, the PPDU of FIG. 12 includes various fields, each of which corresponds to the field shown in FIG. 2, FIG. 3, and FIG. 7. Meanwhile, as shown in the figure, the HE TB PPDU (or uplink PPDU) of FIG. 12 may not include the HE-SIG-B field but only the HE-SIG-A field.

1. CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance)

In IEEE 802.11, communication is achieved in a shared wireless medium, and thus has a characteristic fundamentally different from a wired channel environment. For example, communication is possible based on carrier sense multiple access/collision detection (CSMA/CD) in the wired channel environment For example, when a signal is transmitted one time in Tx, the signal is transmitted to Rx without significant signal attenuation since a channel environment does not change much. In this case, when a collision occurs in two or more signals, it is detectable. This is because power detected in Rx is instantaneously greater than power transmitted in Tx. However, in a wireless channel environment, a channel is affected by various factors (e.g., a signal may be significantly attenuated according to a distance or may instantaneously experience deep fading), carrier sensing cannot be achieved correctly in Tx as to whether a signal is properly transmitted in Rx in practice or whether a collision exists. Therefore, a distributed coordination function (DCF) which is a carrier sense multiple access/collision avoidance (CSMA/CA) mechanism is introduced in 802.11. Herein, stations (STAs) having data to be transmitted perform clear channel assessment (CCA) for sensing a medium during a specific duration (e.g., DIFS: DCF inter-frame space) before transmitting the data. In this case, if the medium is idle, the STA can transmit the data by using the medium. On the other hand, if the medium is busy, under the assumption that several STAs have already waited for the use of the medium, the data can be transmitted after waiting by a random backoff period in addition to the DIFS. In this case, the random backoff period can allow the collision to be avoidable because, under the assumption that there are several STAs for transmitting data, each STA has a different backoff interval probabilistically and thus eventually has a different transmission time. When one STA starts transmission, the other STAs cannot use the medium.

The random backoff time and the procedure will be simply described as follows. When a specific medium transitions from busy to idle, several STAs start a preparation for data transmission. In this case, to minimize a collision, the STAs intending to transmit the data select respective random backoff counts and wait by those slot times. The random backoff count is a pseudo-random integer value, and one of uniform distribution values is selected in the range of [0 CW]. Herein, CW denotes a contention window. A CW parameter takes a CWmin value as an initial value, and when transmission fails, the value is doubled. For example, if an ACK response is not received in response to a transmitted data frame, it may be regarded that a collision occurs. If the CW value has a CWmax value, the CWmax value is maintained until data transmission is successful, and when the data transmission is successful, is reset to the CWmin value. In this case, the values CW, CWmin, and CWmax are preferably maintained to 2^(n)−1 for convenience of implementations and operations. Meanwhile, if the random backoff procedure starts, the STA selects the random backoff count in the [0 CW] range and thereafter continuously monitors a medium while counting down a backoff slot. In the meantime, if the medium enters a busy state, the countdown is stopped, and when the medium returns to an idle state, the countdown of the remaining backoff slots is resumed.

2. PHY Procedure

A PHY transmit/receive procedure in Wi-Fi is as follows, but a specific packet configuration method may differ. For convenience, only 11n and 11ax will be taken for example, but 11g/ac also conforms to a similar procedure.

That is, in the PHY transmit procedure, a MAC protocol data unit (MPDU) or an aggregate MPDU (A-MPDU) transmitted from a MAC end is converted into a single PHY service data unit (PSDU) in a PHY end, and is transmitted by inserting a preamble, tail bits, and padding bits (optional), and this is called a PPDU.

The PHY receive procedure is usually as follows. When performing energy detection and preamble detection (L/HT/VHT/HE-preamble detection for each WiFi version), information on a PSDU configuration is obtained from a PHY header (L/HT/VHT/HE-SIG) to read a MAC header, and then data is read.

3. Multi-Band(or Multi-Link) Aggregation

In order to increase a peak throughput, transmission of an increased stream is considered in a WLAN 802.11 system by using a wider band or more antennas compared to the legacy 11a. In addition, a method of using various bands by aggregating the bands is also considered.

The present specification proposes a scheme of transmitting data of HE STAs and HE STAs simultaneously by using the same MU PPDU in a situation of considering a wide bandwidth, a multi-band (or multi-link) aggregation, or the like.

FIG. 13 illustrates multiple channels allocated in a 5 GHz band.

Hereinafter, a “band” may include, for example, 2.4 GHz, 5 GHz, and 6 GHz bands. For example, the 2.4 GHz band and the 5 GHz band are supported in the 11n standard, and up to the 6 GHz band is supported in the 11ax standard. For example, in the 5 GHz band, multiple channels may be defined as shown in FIG. 13.

The WLAN system to which technical features of the present specification are applied may support a multi-band. That is, a transmitting STA can transmit a PPDU through any channel (e.g., 20/40/80/80+80/160/240/320 MHz, etc.) on a second band (e.g., 6 GHz) while transmitting the PPDU through any channel (e.g., 20/40/80/80+80/160 MHz, etc.) on a first band (e.g., 5 GHz) (In the present specification, a 240 MHz channel may be a continuous 240 MHz channel or a combination of discontinuous 80/160 MHz channels. Further, a 320 MHz channel may be a continuous 320 MHz channel or a combination of discontinuous 80/160 MHz channels. For example, in the present document, the 20 MHz channel may be a continuous 240 MHz channel, an 80+80+80 MHz channel, or an 80+160 MHz channel).

In addition, the multi-band described in the present document can be interpreted in various meanings. For example, the transmitting STA may set any one of 20/40/80/80+80/160/240/320 MHz channels on the 6 GHz band to the first band, set any one of other 20/40/80/80+80/160/240/320 MHz channels on the 6 GHz band to the second band, and may perform multi-band transmission (i.e., transmission simultaneously supporting the first band and the second band). For example, the transmitting STA may transmit the PPDU simultaneously through the first band and the second band, and may transmit it through only any one of the bands at a specific timing.

At least any one of primary 20 MHz and secondary 20/40/80/160 MHz channels described below may be transmitted in the first band, and the remaining channels may be transmitted in the second band. Alternatively, all channels may be transmitted in the same one band.

In the present specification, the term “band” may be replaced with “link”.

Next, a control signaling method for multi-band aggregation will be described. Since the control signaling method may employ a fast session transfer (FST) setup method, an FST setup protocol will be described below.

The FST setup protocol consists of four states and a rule for a method of transitioning from one state to a next state. The four states are Initial, Setup Completed, Transition Done, and Transition Confirmed. In the Initial state, an FST session operates in one or two bands/channels. In the Setup Complete state, an initiator and a responder are ready to change band/channel(s) currently operating. The FST session may be transferred entirely or partially to another band/channel. The Transition Done state allows the initiator and responder to operate in different bands/channels when a value of link loss timeout (LLT) is 0. Both the initiator and the responder shall communicate successfully in a new band/channel to reach the Transition Confirmed state. A state transition diagram of the FST setup protocol is shown in FIG. 14.

FIG. 14 illustrates four states of the FST setup protocol.

FIG. 15 illustrates a procedure of the FST setup protocol.

FIG. 15 illustrates a procedure of the FST setup protocol for driving a state machine shown in FIG. 14. The procedure of FIG. 15 is an example of a basic procedure, and does not cover all possible usages of the protocol. In FIG. 15, a MAC layer management entity (MLME) 1 and an MLME 2 represent any two MLMEs of a device in which a multi-band is possible according to a reference model described in a reference model for a multi-band operation. As will be described later, FST Setup Request and FST Setup Response frames are exchanged optionally in a repeated manner until an FST initiator and an FST responder move successfully in a Setup Completed state. An operation of the procedure of the FST setup protocol is exemplified in FIG. 15.

In order to establish an FST session in an Initial state and to transfer it in the Setup Completed state of the FST setup protocol, the initiator and the responder shall exchange FST Setup Request and FST Setup Response frames. The FST session exists in the Setup Completed state, a Transition Done state, or a Transition Confirmed state. In the Initial state and the Setup Completed state, an old band/channel represents a frequency band/channel on which the FST session is transferred, and a new band/channel represents a frequency band/channel on which the FST session is transferred. In the Transition Done state, the new band/channel represents a frequency band/channel on which FST Ack Request and FST Ack Response frames are transmitted, and the old band/channel represents a frequency band/channel on which the FST session is transferred.

If the responder accepts the FST Setup Request, a Status Code field is set to SUCCESS, and a Status Code is set to REJECTED_WITH_SUGGESTED_CHANGES. Thus, one or more parameters of the FST Setup Request frame are invalid, and a replacement parameter shall be proposed. In addition, the responder sets the Status Code field to PENDING_ADMITTING_FST_SESSION or PENDING_GAP_IN_BA_WINDOW to indicate that the FST Setup Request is pending, and sets the Status Code field to REQUEST_DECLINED to reject the FST Setup Request frame.

A responder which is an enabling STA sets a Status Code to REJECT_DSE_BAND and thus is initiated by a dependent STA which requests to switch to a frequency band subject to a DSE procedure. Therefore, it is indicated that the FST Setup Request frame is rejected. In this case, if a responder is an enabling STA for the dependent STA, the responder may indicate a duration in a TU before an FST setup starts with respect to the dependent STA by including a Timeout Interval element in the FST Setup Response frame. A Timeout Interval Type field in the Timeout Interval element shall be set to 4. The responder may use a parameter in the FST Setup Request frame received from the dependent STA to initiate the FST setup with respect to the initiator.

A responder which is a dependent STA and which is not enabled shall reject all FST Setup Request frames received for switching to a frequency band subject to the DSE procedure, except for a case where a transmitter of the FST setup Request frame is an enabling STA of the dependent STA.

4. Embodiments Applicable to the Present Disclosure

FIG. 16 illustrates an example of multi-band aggregation using a 2.4 GHz band and a 5 GHz band.

Referring to FIG. 16, an AP and a STA may transmit and receive data through aggregation of the 2.4 GHz band and the 5 GHz band. Multi-band aggregation may be performed using not only 2.4./5 GHz but also any bands ranging from 1 to 7.125 GHz, and aggregation may also be performed using a plurality of RFs within the same band (e.g., 5 GHz). Therefore, there is an opportunity to use not only a bandwidth used in legacy 802.11 but also a bandwidth of 160 MHz or more (e.g., 320 MHz) by employing multi-band aggregation or a plurality of RFs within the same band.

In order to conduct conventional contention in a structure illustrated in FIG. 16, backoff is performed for one designated 20 MHz primary channel (Primary 20 or P20) regardless of a multi-band, and a transmission bandwidth is determined by determining whether a secondary channel is idle/busy during a previous PIFS (or DIFS) at a moment when transmission is possible in P20 (backoff count=0).

However, as a considerably wide bandwidth of 160 MHz or more can be used, a secondary channel having a wide bandwidth, such as a 160 MHz secondary channel (Secondary 160) and a 320 MHz secondary channel (Secondary 320), may exist. Particularly, in a dense environment, the secondary channel is highly likely to be busy and thus is remarkably less likely to be available. Further, when CCA is performed on the secondary channel according to a legacy CCA rule (Primary 20->Secondary 20->Secondary 40 . . . ), the legacy rule cannot be used in a band aggregation combination (e.g., 120 (40+80) MHz, 240 (80+160) MHz, and the like) other than that in 20/40/80/160/320 MHz.

Therefore, to solve the foregoing problems, the present disclosure proposes a contention method in which a primary channel is assigned for each band (or RF).

FIG. 17 illustrates an example in which a primary channel exists in each band (or RF) when performing multi-band aggregation.

As illustrated in FIG. 17, when 160 MHz of a 5 GHz band and 160 MHz of a 6 GHz band are aggregated, P20 exists in each band, in which P20 may exist regardless of a bandwidth size (20 MHz or more) applied in each band (or RF).

Basically, a Wi-Fi system performs contention based on one P20, and an EDCA function (EDCAF) requires a contention window (CW) value and a backoff count (BC) randomly selected in a range from 0 to CW for contention for each access category (AC). Therefore, when there is a plurality of primary channels, that is, when a primary channel exists in each band (or RF), a new contention rule is required for frame transmission, and a CW and a BC may be applied as follows.

A. To apply common CW to all P20s and separate BC to each P20

->In method A, a legacy BC decrement rule for each primary channel can be flexibly applied, while more processing overhead is required. Further, a CW adjustment method depending on success in transmission in each band is additionally required.

B. To apply common CW and common BC to all P20s

->In method B, one CW and one BC can be maintained as conventionally regardless of the number of primary channels, while a new BC decrement rule is required according to the channel state of each P20.

C. To apply separate CW to each P20 and separate BC to each P20

->In method C, the legacy BC decrement rule for each primary channel and a legacy CW adjustment method depending on success in transmission can be flexibly applied, while more processing overhead is required.

When method B is applied, the BC decrement rule may be applied as follows.

1) To reduce BC value when channel states of all P20s are idle

->Since all P20s are viewed in an integrated manner, the probability of a collision may be reduced, but transmission latency may be increased.

2) To reduce BC value when channel state of at least one of all P20s is idle

->1) Although transmission latency may be reduced compared to method 1), the probability of a collision may increase because another busy P20 is ignored.

5. Proposed Embodiments

The present disclosure relates to a method for sharing a channel state to solve a hidden node problem in flexible DL/UL transmission in a WLAN (802.11) system.

FIG. 18 illustrates an example of a FDU transmission method.

Flexible DL/UL (FDU) transmission is a technique enabling simultaneous Tx/Rx in a multi-band environment and can increase average BSS throughput. FIG. 18 shows an example of FDU transmission, in which STA 1 performs UL transmission to an AP through band 1 while the AP is performing DL transmission to STA 3 through band 2.

FDU transmission enables flexible Tx/Rx but has a hidden node problem that also occurs in existing Wi-Fi.

FIG. 19 illustrates a hidden node problem that occurs in a FDU transmission method.

FIG. 19 shows an example of a hidden node problem in which STA 1 and STA 2 are in a hidden relationship. When STA 2 transmits a UL frame to an AP through band B, the AP recognizes the transmission and thus transmits a DL frame through backoff only in band A. However, STA 1 is in a hidden relationship with STA 2 and thus cannot recognize the transmission by STA 2 through band B. Accordingly, when STA 1 transmits a UL frame through band B, a collision with the UL frame from STA 2 occurs.

To solve the above problem, RTS/CTS may be used according to a conventional art, but a different method may be used in FDU transmission to reduce overhead. In particular, since FDU transmission enables flexible transmission in each band, there is an opportunity to notify in advance the channel state of a band in another band. Therefore, in order to solve a hidden node problem, the present disclosure proposes a method of sharing information on the current channel state of a band when a PPDU is transmitted in another band for transmitting data.

In the present disclosure, a band for sharing a channel state is referred to as a transmission band, and a band corresponding to a channel state to be shared is referred to as a shared band. For example, in FIG. 19, since AP can notify the channel state of band B during DL transmission in band A, a transmission band is band A, and a shared band is band B. Since channel state information needs to be shared between all STAs within coverage rather than specific STAs, the channel state information may be included in a PHY header, thereby transmitting a PPDU. Information that can be included is as follows, one piece of individual information needs to be included per band, and band and/or channel information may be additionally included if an indicator is required.

5.1 Multi-Band CCA Information (One Bit for Each Band)

-   -   CCA information: Can indicate only whether data is being         transmitted (interference) in the shared band. That is, this         information indicates only whether the current channel state is         idle/busy (e.g., 1 indicates idle and 0 indicates busy).     -   NAV length information: Only one bit is required for each band.         However, since the length of a frame transmitted in the shared         band or a TXOP cannot be known, it is necessary to determine a         time until which a NAV needs to be configured. In this case, the         value of the NAV may be the length of a frame being transmitted         in the transmission band or may be a transmission TXOP.

In a hidden node environment (STA 1 and STA 2 in FIG. 19), when the end time of the frame transmitted in the shared band is later than the end time of the NAV, a collision may occur, and when the end time of the frame transmitted in the shared band is earlier than the end time of the NAV, a transmission opportunity may be partly missed but the probability of a collision may be reduced by protection through information sharing.

FIG. 20 illustrates an example of setting a NAV value based on multi-band CCA information.

FIG. 20 shows an example of method 5.1 (a NAV is set to the length of a frame being transmitted in a transmission band) when STA 1 and STA 2 are in a hidden relationship. When AP transmits a frame to STA 3, the AP may indicate ‘11’ in a PHY header (e.g., SIG-A), thereby indicating that band A and band C are currently idle. Next, when the AP transmits a frame to STA 1, the AP may indicate ‘00’ in a PHY header, thereby indicating that band B and band C are busy. In band B, STA 1 can recognize the frame transmitted to STA 3 and can thus configure a NAV for the transmission as in a conventional art. However, in band C, STA 1 cannot recognize a frame transmitted by STA 2 (UL frame transmitted by STA 2) that is hidden, but can know that band C is busy, and can thus configure a NAV until the end of the DL frame. Therefore, there is no collision in band C.

5.2 Multi-Band Transmission Duration Information (NAV Information for Each Band)

-   -   NAV length information: To configure a NAV in a shared band, the         duration of a PPDU being transmitted in the shared band or TXOP         duration information may be indicated. This information does not         include a duration value as it is but includes information on a         length of the duration value excluding time between the start         point of the PPDU or TXOP and the transmission start point of a         transmission band.

It is possible to protect the PPDU being transmitted. However, when a plurality of frames is transmitted within the TXOP, if only the length of the PPDU is indicated rather than the TXOP, a PPDU subsequently transmitted may not be protected.

FIG. 21 illustrates an example of a field defined to share multi-band transmission duration information.

Referring to FIG. 21, when there is one granularity (information amount), no separate indication is needed, and when there are two granularities, a granularity subfield is used for indication. The size of a duration subfield may vary depending on granularity, and it is difficult to express an accurate value as granularity increases. For example, when there is no granularity subfield, granularity is set to 64 μs, and the duration subfield is four bits, duration of up to 15*64=960 μs may be expressed.

FIG. 22 illustrates an example of sharing PPDU duration in an FDU transmission method.

Referring to FIG. 22, since UL transmission of STA 2 is started first in band B, an AP may notify STA 1 of information on the transmission through DL transmission in band A. Here, the information is information about a duration of PPDU duration of STA 2 excluding T_(d), which is the difference between the transmission start time of a DL frame from the AP and the transmission start time of a UL frame from STA 2, and STA 1 receives the information through a PHY header of the DL frame from the AP and configures a NAV corresponding to the duration. For example, when the duration is 1 ms, a duration field is five bits, and granularity is set to 64 μs, the field may be expressed as a value of ‘00001’.

FIG. 23 illustrates an example of sharing a TXOP in an FDU transmission method.

Referring to FIG. 23, since UL transmission of STA 2 is started first in band B, an AP may notify STA 1 of information on the transmission through DL transmission in band A. Here, the information is information about a duration of a TXOP of STA 2 excluding T_(d), which is the difference between the transmission start time of a DL frame from the AP and the transmission start time of a UL frame from STA 2, and STA 1 receives the information through a PHY header of the DL frame from the AP and configures a NAV corresponding to the duration. For example, in a case where granularity is one bit (0:8 μs and 1:64 μs) and a duration field is five bits, when the granularity is 8 μs, duration information in a range of 0 (000000′) to 248 μs (011111′) may be indicated, and when the granularity is 64 μs, duration information in a range of 252 (100000′) to 2172 μs (101111) may be indicated. When the duration information is 2 ms, the field may be expressed as a value of ‘100111’.

Hereinafter, a method for indicating information on the state of a channel to be shared using a MAC header will be described.

Although channel state information on a shared band is shared via a PHY header in the foregoing method, there may be a case where a channel state or a NAV value is indicated to a specific STA rather than all STAs within coverage. In this case, the channel state or the NAV value may be indicated using a new control frame or an existing control frame or may be indicated through a MAC header. Specific methods are illustrated below.

1) Use of New Control Frame or Existing Control Frame

Prior to data transmission, a new control frame may be transmitted for indication and includes content as follows.

-   -   NAV value or channel state (i.e., 1 for busy and 0 for idle         other than NAV value)     -   Information on a band and/or channel that can be additionally         included when an indicator is needed

The new control frame including the content may operate as follows. The interval of each frame is SIFS but is not limited thereto.

i) The new control frame is transmitted.

ii) A reception STA may transmit an immediate response frame if necessary. For example, when the new control frame operates like a CTS-to-self frame, the reception STA may not transmit an immediate response frame.

iii) A transmission STA may transmit data after receiving an immediate response frame or transmitting the new control frame.

FIG. 24 illustrates an example of an operation process of a new control frame.

Referring to FIG. 24, when an AP is receiving a UL frame from STA 2 in band B, the AP notifies STA 1 of information through the foregoing content in a control frame and then transmits data to STA 1 after SIFS.

Further, an existing control frame (e.g., a RTS/CTS-to-self frame or the like) may be used, and the following content may be included by adding a bit to the existing control frame or by employing a reserved bit.

-   -   NAV value or channel state (i.e., 1 for busy and 0 for idle         other than NAV value)     -   Information on a band and/or channel that can be additionally         included when an indicator is needed

2) New Control Field Type

When data is transmitted, a new control field may be added to a MAC header for indication and may include the following content.

-   -   NAV value or channel state (i.e., 1 for busy and 0 for idle         other than NAV value)     -   Information on a band and/or channel that can be additionally         included when an indicator is needed

3) Use of Reserved Bit in Existing Control Field

An AP may indicate channel state information using a reserved bit for each control ID existing in an existing A-Control field of a MAC header, and the following content is included for each control ID.

i) Reserved bit of TRS/HLA control field (one bit)

-   -   Channel state (i.e., 1 for busy and 0 for idle)     -   The channel state of only one band/channel can be indicated         rather than those of bands/channels.

ii) Reserved bit of UPH/BQR control field (two bits)

-   -   Channel state (i.e., 1 for busy and 0 for idle)     -   Information on a band and/or channel that can be additionally         included when an indicator is needed     -   It is possible to indicate the channel states of up to two         bands/channels, but when band/channel information is included,         the channel state of only one band/channel can be indicated.

iii) Reserved bit of CAS control field (five bits)

-   -   NAV value or channel state (i.e., 1 for busy and 0 for idle         other than NAV value)     -   Information on a band and/or channel that can be additionally         included when an indicator is needed     -   NAV duration can have a length of up to five bits.

Hereinafter, the embodiments described above with reference to FIG. 14 to FIG. 24 are illustrated.

FIG. 25 is a flowchart illustrating a procedure in which a transmission device transmits and receives a frame according to an embodiment.

The embodiment of FIG. 25 may be performed in a network environment supporting a next-generation WLAN system. The next-generation WLAN system may be a WLAN system evolving from an 802.11ax system and may satisfy backward compatibility with the 802.11ax system. The next-generation WLAN system may correspond to an extremely high throughput (EHT) WLAN system or an 802.11be WLAN system.

The embodiment proposes a method for sharing a channel state to solve a hidden node problem when flexible DL/UL transmission using multi-band aggregation is performed in a next-generation WLAN, such as an EHT WLAN system.

The embodiment of FIG. 25 may be performed by an access point (AP), and a first station (STA) and a second STA of FIG. 25 may correspond to STAs supporting an EHT WLAN system. The AP and the first STA may support a multi-band (or multi-link).

In operation S2510, the AP transmits a first frame to the first STA through a first band.

In operation S2520, the AP receives a second frame from the second STA through a second band while transmitting the first frame.

The first band and the second band may be aggregated into a multi-band. The first band includes a first primary channel, and the second band includes a second primary channel.

When the multi-band includes only the two bands which are aggregated, the first band may be a 2.4 GHz or 5 GHz band, and the second band may be a 6 GHz band. When the multi-band further include a third band, the first band may be a 2.4 GHz band, the second band may be a 5 GHz band, and the third band may be a 6 GHz band. The foregoing configurations of the bands are provided only for illustration, and the WLAN system may support various numbers of bands and channels.

The multi-band simultaneously supports DL transmission and UL transmission. This is called flexible DL/UL (FDU) transmission, and FDU transmission is a transmission technique enabling simultaneous Tx/Rx in a multi-band to increase average BSS throughput.

The first STA and the second STA are in a hidden node relationship. Thus, the first STA cannot recognize transmission by the second STA through the second band. If the first STA transmits a third frame through the second band, a collision with the second frame transmitted by the second STA occurs. This embodiment proposes a method of sharing channel state information on a different band in a specific band in order to prevent a data collision between STAs in a hidden node relationship. Here, the channel state information is included in a physical (PHY) header in order to share the channel state information with all STAs within BSS coverage.

Specifically, a PHY header of the first frame includes channel state information on the second band. Accordingly, a NAV for the first STA is configured based on the channel state information.

For example, when the channel state of the second band is idle based on the channel state information, the NAV for the first STA may not be configured. In this case, it is assumed that no frame is transmitted in the second band while the first frame is being transmitted. Since the channel state of the second band is idle, the first STA may transmit the third frame through the second band without needing to configure a NAV.

In another example, when the channel state of the second band is busy based on the channel state information, the NAV for the first STA may be configured until the transmission of the first frame ends, which means that since the second frame is received in the second band while the first frame is being transmitted, the channel state of the second band is busy. Accordingly, the first STA configures the NAV, thereby not transmitting the third frame through the second band until the transmission of the first frame ends.

The PHY header may further include transmission duration information on the multi-band.

The transmission duration information may include a granularity subfield and a duration subfield. The maximum length of the duration subfield may be determined based on the value of the granularity subfield. For example, when the value of the granularity subfield is 64 μs and the duration subfield is 4 bits, the maximum length that can be indicated by the duration subfield may be 15*64=960 μs.

The duration subfield may include first duration information or second duration information.

The first duration information may be information on the length of transmission duration of the second frame excluding Td. The second duration information may be information on the length of a transmission opportunity (TXOP) for the second STA excluding Td.

Td may be a length equal to the difference between the transmission start time of the second frame and the transmission start time of the first frame. That is, the transmission duration information may include information on the length (time) of a frame or TXOP duration excluding Td rather than including a frame or TXOP duration value as it is.

The NAV for the first STA may be set to be equal to the length of the first duration information (duration of the second frame—Td) or the length of the second duration information (TXOP duration of the second STA—Td).

The AP may receive the third frame from the first STA through the second band after the NAV for the first STA. Accordingly, the first STA may transmit the third frame through the second band without a collision with the second frame.

Hereinafter, a signaling method for multi-band aggregation is described. In this embodiment, configuration information on the multi-band is described as being received, and signaling may be performed by employing an FST setup method.

A transmission device and a reception device to be illustrated below may correspond to the AP or the first and second STAs illustrated above. The transmission device may transmit a multi-band setup request frame to the reception device. The transmission device may receive a multi-band setup response frame from the reception device.

The transmission device may transmit a multi-band ACK request frame to the reception device. The transmission device may receive a multi-band ACK response frame from the reception device.

The transmission device may include a first station management entity (SME), a first MAC layer management entity (MLME), and a second MLME. The reception device may include a second SME, a third MLME, and a fourth MLME.

The first MLME and the third MLME may be entities supporting the first band, and the second MLME and the fourth MLME may be entities supporting the second band.

The multi-band setup request frame and the multi-band setup response frame may be transmitted and received between the first MLME and the third MLME. The multi-band ACK request frame and the multi-band ACK response frame may be transmitted and received between the second MLME and the fourth MLME.

The first and the second SMEs may generate a primitive including a multi-band parameter. The multi-band parameter may include a channel number designated in the multi-band, an operating class, and a band identifier (ID). The primitive may be transmitted to the first to fourth MLMEs.

When the FST setup method is employed for the multi-band aggregation, the FST setup method includes four states and a rule for a method of transitioning one state to a next state. The four states are Initial, Setup Completed, Transition Done, and Transition Confirmed states.

In the Initial state, the transmission device and the reception device communicate in an old band/channel. Here, when an FST setup request frame an FST setup response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Setup Completed state and are ready to change the currently operating band/channel(s). An FST session may be entirely or partially transferred to another band/channel.

When an LLT value included in the FST setup request frame is 0, the transmission device and the reception device transition from the Setup Completed state to the Transition Done state and are allowed to operate in different bands/channels.

Both the transmission device and the reception device need to succeed in communication in a new band/channel to reach the Transition Confirmed state. Here, when an FST ACK request frame and an FST ACK response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Transition Confirmed state and establish a complete connection in the new band/channel.

FIG. 26 is a flowchart illustrating a procedure in which a reception device transmits and receives a frame according to an embodiment.

The embodiment of FIG. 26 may be performed in a network environment supporting a next-generation WLAN system. The next-generation WLAN system may be a WLAN system evolving from an 802.11ax system and may satisfy backward compatibility with the 802.11ax system. The next-generation WLAN system may correspond to an extremely high throughput (EHT) WLAN system or an 802.11be WLAN system.

The embodiment proposes a method for sharing a channel state to solve a hidden node problem when flexible DL/UL transmission using multi-band aggregation is performed in a next-generation WLAN, such as an EHT WLAN system.

The embodiment of FIG. 26 may be performed by a first station (STA), and the first STA and a second STA may correspond to STAs supporting an EHT WLAN system. An access point (AP) and the first STA of FIG. 26 may support a multi-band (or multi-link).

In operation S2610, the first STA receives a first frame from the AP through a first band. While the first frame is being received, a second frame is transmitted from the second STA to the AP through a second band.

In operation S2620, the first STA configures a NAV based on channel state information on the second band.

The first band and the second band may be aggregated into a multi-band. The first band includes a first primary channel, and the second band includes a second primary channel.

When the multi-band includes only the two bands which are aggregated, the first band may be a 2.4 GHz or 5 GHz band, and the second band may be a 6 GHz band. When the multi-band further include a third band, the first band may be a 2.4 GHz band, the second band may be a 5 GHz band, and the third band may be a 6 GHz band. The foregoing configurations of the bands are provided only for illustration, and the WLAN system may support various numbers of bands and channels.

The multi-band simultaneously supports DL transmission and UL transmission. This is called flexible DL/UL (FDU) transmission, and FDU transmission is a transmission technique enabling simultaneous Tx/Rx in a multi-band to increase average BSS throughput.

The first STA and the second STA are in a hidden node relationship. Thus, the first STA cannot recognize transmission by the second STA through the second band. If the first STA transmits a third frame through the second band, a collision with the second frame transmitted by the second STA occurs. This embodiment proposes a method of sharing channel state information on a different band in a specific band in order to prevent a data collision between STAs in a hidden node relationship. Here, the channel state information is included in a physical (PHY) header in order to share the channel state information with all STAs within BSS coverage.

Specifically, a PHY header of the first frame includes channel state information on the second band. Accordingly, a NAV for the first STA is configured based on the channel state information.

For example, when the channel state of the second band is idle based on the channel state information, the NAV for the first STA may not be configured. In this case, it is assumed that no frame is transmitted in the second band while the first frame is being transmitted. Since the channel state of the second band is idle, the first STA may transmit the third frame through the second band without needing to configure a NAV.

In another example, when the channel state of the second band is busy based on the channel state information, the NAV for the first STA may be configured until the transmission of the first frame ends, which means that since the second frame is received in the second band while the first frame is being transmitted, the channel state of the second band is busy. Accordingly, the first STA configures the NAV, thereby not transmitting the third frame through the second band until the transmission of the first frame ends.

The PHY header may further include transmission duration information on the multi-band.

The transmission duration information may include a granularity subfield and a duration subfield. The maximum length of the duration subfield may be determined based on the value of the granularity subfield. For example, when the value of the granularity subfield is 64 μs and the duration subfield is 4 bits, the maximum length that can be indicated by the duration subfield may be 15*64=960 μs.

The duration subfield may include first duration information or second duration information.

The first duration information may be information on the length of transmission duration of the second frame excluding Td. The second duration information may be information on the length of a transmission opportunity (TXOP) for the second STA excluding Td.

Td may be a length equal to the difference between the transmission start time of the second frame and the transmission start time of the first frame. That is, the transmission duration information may include information on the length (time) of a frame or TXOP duration excluding Td rather than including a frame or TXOP duration value as it is.

The NAV for the first STA may be set to be equal to the length of the first duration information (duration of the second frame—Td) or the length of the second duration information (TXOP duration of the second STA—Td).

The AP may receive the third frame from the first STA through the second band after the NAV for the first STA. Accordingly, the first STA may transmit the third frame through the second band without a collision with the second frame.

Hereinafter, a signaling method for multi-band aggregation is described. In this embodiment, configuration information on the multi-band is described as being received, and signaling may be performed by employing an FST setup method.

A transmission device and a reception device to be illustrated below may correspond to the AP or the first and second STAs illustrated above. The transmission device may transmit a multi-band setup request frame to the reception device. The transmission device may receive a multi-band setup response frame from the reception device.

The transmission device may transmit a multi-band ACK request frame to the reception device. The transmission device may receive a multi-band ACK response frame from the reception device.

The transmission device may include a first station management entity (SME), a first MAC layer management entity (MLME), and a second MLME. The reception device may include a second SME, a third MLME, and a fourth MLME.

The first MLME and the third MLME may be entities supporting the first band, and the second MLME and the fourth MLME may be entities supporting the second band.

The multi-band setup request frame and the multi-band setup response frame may be transmitted and received between the first MLME and the third MLME. The multi-band ACK request frame and the multi-band ACK response frame may be transmitted and received between the second MLME and the fourth MLME.

The first and the second SMEs may generate a primitive including a multi-band parameter. The multi-band parameter may include a channel number designated in the multi-band, an operating class, and a band identifier (ID). The primitive may be transmitted to the first to fourth MLMEs.

When the FST setup method is employed for the multi-band aggregation, the FST setup method includes four states and a rule for a method of transitioning one state to a next state. The four states are Initial, Setup Completed, Transition Done, and Transition Confirmed states.

In the Initial state, the transmission device and the reception device communicate in an old band/channel. Here, when an FST setup request frame an FST setup response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Setup Completed state and are ready to change the currently operating band/channel(s). An FST session may be entirely or partially transferred to another band/channel.

When an LLT value included in the FST setup request frame is 0, the transmission device and the reception device transition from the Setup Completed state to the Transition Done state and are allowed to operate in different bands/channels.

Both the transmission device and the reception device need to succeed in communication in a new band/channel to reach the Transition Confirmed state. Here, when an FST ACK request frame and an FST ACK response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Transition Confirmed state and establish a complete connection in the new band/channel.

6. Device Configuration

FIG. 27 is a diagram illustrating a device for implementing the aforementioned method.

A wireless device (100) of FIG. 27 may be a transmission device capable of implementing the foregoing embodiments and may operate as an AP STA. A wireless device (150) of FIG. 27 may be a reception device capable of implementing the foregoing embodiments and may operate as a non-AP STA.

The transmission device (100) may include a processor (110), a memory (120), and a transceiver (130), and the reception device (150) may include a processor (160), a memory (170), and a transceiver (180). The transceiver (130, 180) transmits/receives a radio signal and may be operated in a physical layer of IEEE 802.11/3GPP, and so on. The processor (110, 160) may be operated in the physical layer and/or MAC layer and may be operatively connected to the transceiver (130, 180).

The processor (110, 160) and/or the transceiver (130, 180) may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processor. The memory (120, 170) may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage unit. When the embodiments are executed by software, the techniques (or methods) described herein can be executed with modules (e.g., processes, functions, and so on) that perform the functions described herein. The modules can be stored in the memory (120, 170) and executed by the processor (110, 160). The memory (120, 170) can be implemented (or positioned) within the processor (110, 160) or external to the processor (110, 160). Also, the memory (120, 170) may be operatively connected to the processor (110, 160) via various means known in the art.

The processor (110, 160) may implement the functions, processes and/or methods proposed in the present disclosure. For example, the processor (110, 160) may perform the operation according to the present embodiment.

A specific operation of the processor (110) of the transmission device is as follows. The processor (110) of the transmission device transmits a first frame to a first STA through a first band, and receives a second frame from a second STA through a second band while transmitting the first frame.

A specific operation of the processor (160) of the reception device is as follows. The processor (160) of the reception device receives a first frame from an AP through a first band and configures a NAV base on channel state information on a second band. While the first frame is being received, a second frame is transmitted from a second STA to the AP through the second band.

FIG. 28 illustrates a specific wireless device for implementing an embodiment of the present disclosure. The present disclosure described above with respect to a transmission device or a reception device may be applied to this embodiment.

A wireless device includes a processor 610, a power management module 611, a battery 612, a display 613, a keypad 614, a subscriber identification module (SIM) card 615, a memory 620, a transceiver 630, one or more antennas 631, a speaker 640, and a microphone 641.

The processor 610 may be configured to implement proposed functions, procedures, and/or methods described in this disclosure. Layers of the radio interface protocol may be implemented in the processor 610. The processor 610 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The processor 610 may be an application processor (AP). The processor 610 may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor 610 may be found in SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™ series of processors made by Samsung®, A series of processors made by Apple HELIO™ series of processors made by MediaTek®, ATOM™ series of processors made by Intel® or a corresponding next generation processor.

The power management module 611 manages power for the processor 610 and/or the transceiver 630. The battery 612 supplies power to the power management module 611. The display 613 outputs results processed by the processor 610. The keypad 614 receives inputs to be used by the processor 610. The keypad 614 may be shown on the display 613. The SIM card 615 is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers). It is also possible to store contact information on many SIM cards.

The memory 620 is operatively coupled with the processor 610 and stores a variety of information to operate the processor 610. The memory 620 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory 620 and executed by the processor 610. The memory 620 can be implemented within the processor 610 or external to the processor 610 in which case those can be communicatively coupled to the processor 610 via various means as is known in the art.

The transceiver 630 is operatively coupled with the processor 610, and transmits and/or receives a radio signal. The transceiver 630 includes a transmitter and a receiver. The transceiver 630 may include baseband circuitry to process radio frequency signals. The transceiver 630 controls the one or more antennas 631 to transmit and/or receive a radio signal.

The speaker 640 outputs sound-related results processed by the processor 610. The microphone 641 receives sound-related inputs to be used by the processor 610.

In a transmission device, the processor (610) transmits a first frame to a first STA through a first band, and receives a second frame from a second STA through a second band while transmitting the first frame.

In a reception device, the processor (610) receives a first frame from an AP through a first band and configures a NAV base on channel state information on a second band. While the first frame is being received, a second frame is transmitted from a second STA to the AP through the second band.

The first band and the second band may be aggregated into a multi-band. The first band includes a first primary channel, and the second band includes a second primary channel.

When the multi-band includes only the two bands which are aggregated, the first band may be a 2.4 GHz or 5 GHz band, and the second band may be a 6 GHz band. When the multi-band further include a third band, the first band may be a 2.4 GHz band, the second band may be a 5 GHz band, and the third band may be a 6 GHz band. The foregoing configurations of the bands are provided only for illustration, and the WLAN system may support various numbers of bands and channels.

The multi-band simultaneously supports DL transmission and UL transmission. This is called flexible DL/UL (FDU) transmission, and FDU transmission is a transmission technique enabling simultaneous Tx/Rx in a multi-band to increase average BSS throughput.

The first STA and the second STA are in a hidden node relationship. Thus, the first STA cannot recognize transmission by the second STA through the second band. If the first STA transmits a third frame through the second band, a collision with the second frame transmitted by the second STA occurs. This embodiment proposes a method of sharing channel state information on a different band in a specific band in order to prevent a data collision between STAs in a hidden node relationship. Here, the channel state information is included in a physical (PHY) header in order to share the channel state information with all STAs within BSS coverage.

Specifically, a PHY header of the first frame includes channel state information on the second band. Accordingly, a NAV for the first STA is configured based on the channel state information.

For example, when the channel state of the second band is idle based on the channel state information, the NAV for the first STA may not be configured. In this case, it is assumed that no frame is transmitted in the second band while the first frame is being transmitted. Since the channel state of the second band is idle, the first STA may transmit the third frame through the second band without needing to configure a NAV.

In another example, when the channel state of the second band is busy based on the channel state information, the NAV for the first STA may be configured until the transmission of the first frame ends, which means that since the second frame is received in the second band while the first frame is being transmitted, the channel state of the second band is busy. Accordingly, the first STA configures the NAV, thereby not transmitting the third frame through the second band until the transmission of the first frame ends.

The PHY header may further include transmission duration information on the multi-band.

The transmission duration information may include a granularity subfield and a duration subfield. The maximum length of the duration subfield may be determined based on the value of the granularity subfield. For example, when the value of the granularity subfield is 64 μs and the duration subfield is 4 bits, the maximum length that can be indicated by the duration subfield may be 15*64=960 μs.

The duration subfield may include first duration information or second duration information.

The first duration information may be information on the length of transmission duration of the second frame excluding Td. The second duration information may be information on the length of a transmission opportunity (TXOP) for the second STA excluding Td.

Td may be a length equal to the difference between the transmission start time of the second frame and the transmission start time of the first frame. That is, the transmission duration information may include information on the length (time) of a frame or TXOP duration excluding Td rather than including a frame or TXOP duration value as it is.

The NAV for the first STA may be set to be equal to the length of the first duration information (duration of the second frame—Td) or the length of the second duration information (TXOP duration of the second STA—Td).

The AP may receive the third frame from the first STA through the second band after the NAV for the first STA. Accordingly, the first STA may transmit the third frame through the second band without a collision with the second frame.

Hereinafter, a signaling method for multi-band aggregation is described. In this embodiment, configuration information on the multi-band is described as being received, and signaling may be performed by employing an FST setup method.

A transmission device and a reception device to be illustrated below may correspond to the AP or the first and second STAs illustrated above. The transmission device may transmit a multi-band setup request frame to the reception device. The transmission device may receive a multi-band setup response frame from the reception device.

The transmission device may transmit a multi-band ACK request frame to the reception device. The transmission device may receive a multi-band ACK response frame from the reception device.

The transmission device may include a first station management entity (SME), a first MAC layer management entity (MLME), and a second MLME. The reception device may include a second SME, a third MLME, and a fourth MLME.

The first MLME and the third MLME may be entities supporting the first band, and the second MLME and the fourth MLME may be entities supporting the second band.

The multi-band setup request frame and the multi-band setup response frame may be transmitted and received between the first MLME and the third MLME. The multi-band ACK request frame and the multi-band ACK response frame may be transmitted and received between the second MLME and the fourth MLME.

The first and the second SMEs may generate a primitive including a multi-band parameter. The multi-band parameter may include a channel number designated in the multi-band, an operating class, and a band identifier (ID). The primitive may be transmitted to the first to fourth MLMEs.

When the FST setup method is employed for the multi-band aggregation, the FST setup method includes four states and a rule for a method of transitioning one state to a next state. The four states are Initial, Setup Completed, Transition Done, and Transition Confirmed states.

In the Initial state, the transmission device and the reception device communicate in an old band/channel. Here, when an FST setup request frame an FST setup response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Setup Completed state and are ready to change the currently operating band/channel(s). An FST session may be entirely or partially transferred to another band/channel.

When an LLT value included in the FST setup request frame is 0, the transmission device and the reception device transition from the Setup Completed state to the Transition Done state and are allowed to operate in different bands/channels.

Both the transmission device and the reception device need to succeed in communication in a new band/channel to reach the Transition Confirmed state. Here, when an FST ACK request frame and an FST ACK response frame are transmitted and received between the transmission device and the reception device, the transmission device and the reception device transition to the Transition Confirmed state and establish a complete connection in the new band/channel. 

What is claimed is:
 1. A method for transmitting and receiving a frame in a wireless local area network (WLAN) system, the method comprising: transmitting, by an access point (AP), a first frame to a first station (STA) through a first band; and receiving, by the AP, a second frame from a second STA through a second band while transmitting the first frame, wherein the first band and the second band are aggregated into a multi-band, the multi-band simultaneously supports DL transmission and UL transmission, the first STA and the second STA are in a hidden node relationship, a PHY header of the first frame comprises channel state information on the second band, and a NAV for the first STA is configured based on the channel state information.
 2. The method of claim 1, wherein, when a channel state of the second band is idle based on the channel state information, the NAV for the first STA is not configured.
 3. The method of claim 1, wherein, when a channel state of the second band is busy based on the channel state information, the NAV for the first STA is configured until transmission of the first frame ends.
 4. The method of claim 1, wherein the PHY header further comprises transmission duration information on the multi-band, the transmission duration information comprises a granularity subfield and a duration subfield, and a maximum length of the duration subfield is determined based on a value of the granularity subfield.
 5. The method of claim 4, wherein the duration subfield comprises first duration information or second duration information, the first duration information is information on a length of transmission duration of the second frame excluding Td, the second duration information is information on a length of a transmission opportunity (TXOP) for the second STA excluding Td, and Td is a length equal to a difference between a transmission start time of the second frame and a transmission start time of the first frame.
 6. The method of claim 5, wherein the NAV for the first STA is set to be equal to a length of the first duration information or a length of the second duration information.
 7. The method of claim 1, further comprising: receiving, by the AP, a third frame from the first STA through the second band after the NAV for the first STA.
 8. An access point (AP) for transmitting and receiving a frame in a wireless local area network (WLAN) system, the AP comprising: a memory; a transceiver; and a processor operatively coupled with the memory and the transceiver, wherein the processor transmits a first frame to a first station (STA) through a first band and receives a second frame from a second STA through a second band while transmitting the first frame, the first band and the second band are aggregated into a multi-band, the multi-band simultaneously supports DL transmission and UL transmission, the first STA and the second STA are in a hidden node relationship, a PHY header of the first frame comprises channel state information on the second band, and a NAV for the first STA is configured based on the channel state information.
 9. The AP of claim 8, wherein, when a channel state of the second band is idle based on the channel state information, the NAV for the first STA is not configured.
 10. The AP of claim 8, wherein, when a channel state of the second band is busy based on the channel state information, the NAV for the first STA is configured until transmission of the first frame ends.
 11. The AP of claim 8, wherein the PHY header further comprises transmission duration information on the multi-band, the transmission duration information comprises a granularity subfield and a duration subfield, and a maximum length of the duration subfield is determined based on a value of the granularity subfield.
 12. The AP of claim 11, wherein the duration subfield comprises first duration information or second duration information, the first duration information is information on a length of transmission duration of the second frame excluding Td, the second duration information is information on a length of a transmission opportunity (TXOP) for the second STA excluding Td, and Td is a length equal to a difference between a transmission start time of the second frame and a transmission start time of the first frame.
 13. The AP of claim 12, wherein the NAV for the first STA is set to be equal to a length of the first duration information or a length of the second duration information.
 14. The AP of claim 8, wherein the processor receives a third frame from the first STA through the second band after the NAV for the first STA.
 15. A method for receiving a frame in a wireless local area network (WLAN) system, the method comprising: receiving, by a first station (STA), a first frame from an access point (AP) through a first band, a second frame being transmitted from a second STA to the AP through a second band while the first frame is being received; and configuring, by the first STA, a NAV based on channel state information on the second band, wherein the first band and the second band are aggregated into a multi-band, the multi-band simultaneously supports DL transmission and UL transmission, the first STA and the second STA are in a hidden node relationship, a PHY header of the first frame comprises the channel state information on the second band, and the NAV for the first STA is configured based on the channel state information. 